EDIT: SFort will be continuing to maintain Fabrication, as he has been. I will do this rework in another mod if I get around to it. I've granted him write access in all relevant places and migrated the site to GitHub so I'm no longer getting in the way.

Fabrication has become a massive behemoth that no one is able to adequately maintain, and its large collection of mixins and custom injection code makes maintaining it across versions (and porting it to new versions, such as 1.19.3) essentially impossible. SFort has been taking on the brunt of this while I just kind of pretend the project doesn't exist, but he's run out of time and motivation as well at this point.

I would like Fabrication 4 to focus on stability. Fabrication has garnered a (deserved) reputation for being unstable and buggy — it's simply not possible for us to test and adequately maintain all 261 features, and there's a lot of odd custom injections and reimplementations of Fabric API for no reason. 4 should use standard community libraries, like MixinExtras and Fabric API.

More than that, i feel like the features of the mod could be split into smaller mods. A lot of features target different kinds of players, like modpack makers, server owners, technical players, your average joe schmoe. Maybe if the features were divided in more targeted categories, it would be easier to find mantainers. Huge lists are always disencouraging, specially when you don't care about everything there.

I did a quick sorting of features based on usage cases, as opposed to the current "intrusivity" approach. Might be useful to sort things out.

Creator and Admin tools (No regular player would use these, meant for server admins, mapmakers and modpack makers)

Adventure Tags In Survival
CanHit
/i And More
Inanimates Can Be Invisible
Item Despawn Control
Item Frames Don't Display Name Tags
KillMessage
Legacy Command Syntax
Lenient Command Suggestions
Mob IDs
/mods Command
Ping Privacy
Show Map ID
Taggable Players
Yeet Recipes

Technical Players (Needs deep knowledge of mechanics or at least some familiarity with redstone)

Campfires Cook Entities
ChunkLoading Furnace Minecart
Colorful Redstone
Detecting Powered Rails
Directional Detector Rails
Directional Powered Rails
Exact Note Block Tuning
Flimsy Tripwire
Launching Pistons
Less Restrictive Note Blocks
Note Block Notes
Note Blocks Play On Landing
Observers See Entities
Observers See Entities - Living Only
Play Note Blocks In Creative
Pursurvers
Reverse Note Block Tuning
Spawners Always Tick
Stable Cacti Break Vanilla Compat
Thrown Buckets Empty Lava Cauldrons
Toggleable Furnace Carts

Aesthetic Fixes, Tweaks and Additions (Won't affect too much the server or other players)

Alt Absorption Sound
Better Pause Freezing
Blinking Drops
Block Logo
Boundless Levels
Bubble Column Pop
Billboard Drops
Classic Block Drops
Colored Crack Particles
Cracking Spawn Eggs
Dirt Screen
Disable Equip Sound
Disable Nether Fog
End Portal Parallax
Ender Pearl Sound
Fix End Portal Render
Fix Nether Portal Nausea
Flat Items
Foliage Creepers
Fullres Banner Shields
Ghast Charging
Ghast Panic
Janky Arm
Less Annoying Fire
Long Level Up Sound At 30
Mechanism Muffling
More Explosion Particles
No Hand Sway
No Player Death Animation
No Stance Transition
Normal Fog With Night Vision
Oak Is Apple
Old Background Shade
Old Lava
Old Tooltip
Omniscent Player
Oof
Rainbow Experience
Silent Minecarts
Silverfish Step
Sync Attacker Yaw (Fixed in snapshots)
TNT Is Dynamite
Uncap Menu FPS
Void Fog
Void Fog Particles
Yellow Button Hover

QoL (Mostly related to interfaces or ease of use)

Books Show Enchants
Chat Markdown
Crawling
Despawning Items Blink
Extract Furnace Experience
Faster Obsidian
Fire Aspect Is Flint And Steel
Furnace Minecart Pushing
Gradual Block Breaking
Hide Armor
Linkify Urls
Multiline Sign Paste
Open Inventories in Nether Portals
Recipe Book Auto Craft
RMB Clears Text Fields
Use Player List Name In Tag
See Held Items While Riding
Show Bee Count in Tooltip
Show Bee Count on Items
Stable Cacti
Tools Show Important Enchant
Unsaddle Creatures
Water Fills On Break
Water Fills On Break Strict 

Accessibility and Peace of Mind (Covers edge cases that don't affect most players but might be deal breaking to those affected)

Can Breathe Water
Disable Bees
Disable Prior Work Penalty
Ender Dragon Always Spawns Dragon Egg
Endermen Don't Grief
Endermen Don't Squeal
Environmentally Friendly Creepers
Enter Selects Highlighted Suggestion
Fireproof
Invisible To Mobs
Legible Signs (could be QoL)
No Guardian Jumpscare
No Night Vision Flashing
Permanent Conduit Power
Permanent Dolphins Grace
Toggle Sprint
Toggle Stance
Scares Creepers
Static Dragon Egg

Feature Removal (Quick and Dirty, A.k.a "The best solution to a problem is usually the easiest one")

Anvil No Xp Cost
Bush Walk Doesn't Hurt
Disable Elytra
Disable Elytra Boost
Disable Lightning Fire
Disable Mending
Disable Night Skip
Disable Storing Thrown Ender Pearls
Disable Villagers
No Dolphin Theft
No Experience
No Heavy Minecarts
No Hunger
No Phantoms
No Sneak Bypass
No Sprint
No Swim
No Trample
No Wandering Trader

Nerf-oriented balance (Changes aspects some might consider overpowered or just makes stuff harder)

Brittle Shields
Campfires Place Unlit
Chaining Creepers
Creepers Explode When On Fire
Disable Mending Trade
Drop Experience With keepInventory
Faulty Shields
Full Enchanting Cost
Lava Causes Fall Damage
Nether Cauldron
No Filled Inventories In Shulkers
Mobs Drop Less Metal
Old Armor
Old Armor Scale
Photoresistant Mobs
Villager Trades Reset

Buff-oriented balance (Encourages otherwise unviable tactics or just makes stuff easier)

Anvil Repair
Anvil Fully Repairs
Anvil No Level Limit
Anvil Rename Always Costs One
Anvils Take Damage Only When Falling
Arrows Work In Water
Bedrock-Like Impaling
Broken Gear Drops Components
Bush Walk Doesn't Hurt When Sneaking
Bush Walk Doesn't Hurt With Armor
Cactus Brush Doesn't Hurt With Chest
Cactus Walk Doesn't Hurt With Boots
Channeling Two
Creepers Can't climb
Drop More Experience On Death
Déjà Void
Feather Falling V
Feather Falling V Damages Boots
Feather Falling No Trample
Full Ender Dragon XP
Furnace Minecart Accepts Any Fuel
Hyperspeed Furnace Minecart
InfiBows
Infinity Crossbows
Infinity & Mending
No Dinnerlava
Photoallergic Creepers
Pickup Skeleton Arrows
Soul Speed Doesn't Damage Boots
Spiders Can't Climb Glazed Terracotta
Swap Conflicting Enchants
Tools in Bundles
Tridents Accept Power
Tridents Accept Sharpness
Tridents In Void Return
Use Items While Riding

Two-edged Tweaks (Tweaks that make the game harder or easier depending on the situation)

Campfires Ignite Entities
Collision Based Landing Pos
Flammable Cobwebs
Interrupting Damage
Player Free Spawners
Shulker Bullets Despawn On Death
Source Dependent Invulnerability Frames
Underwater Explosions

Full Mechanics (Complete game changers)

Bottled Air
Curable Piglins
Enhanced Moistness
    Spiders Can't Climb While Wet
Grindstone Disenchanting
Obsidian Tears
Protection On Any Item
Weaponized Pearls

Weird or Situational (Features whose uses are very specific)

All Damage Is Fatal
Blaze Powder Grows Nether Wart
Cactus Punching Hurts
Dimensional Tools
Dropped Items Don't Stack
Encroaching Emeralds
Entities Can't Climb
Fire Protection On Any Item
Fix Charm Amethyst Dupe
Food Always Edible
Instant Bow
Instant Eat
Instant Pickup
Invisibility Splash On Inanimates
Item Safe Cactus
Leaves Grow Grass
Melee Mobs Keep Attacking
Old Sheep Shear
Slow Fall Splash On Inanimates
Spreadable Moss
Tridents Activate Levers
Villagers Follow Emerald Blocks
Weapons Accept Silk
Wool Protected Sheep

The most important features to me are the QoL and aesthetic changes, pixel density consistency is excellent, and while it could be done with a resource pack, doing so would be a massive pain and require a lot of time and effort. Trident void returning is massively important, it's been in Bedrock Edition for ages. Honestly most of the Trident changes are excellent, and make the item much more versatile and usable for how hard it is to get. Being able to crawl on command is MASSIVE for me, and is a very important feature to my personal use, as is blinking items, it lets me see what items to prioritize grabbing and has saved my butt more times than i'd like to admit, especially with its integration with the flashing white. Being able to swap conflicting enchantments is again Huge to my playing, and is a massive help to me in some situations, and actually being able to actually see what enchantments are on an item/book is super massive, as without it I find it nearly impossible to find what enchantments I'm looking for otherwise, same for the Bee count indicator on Bee Home blocks. Reintroducing the ghast "squish" animation is extremely helpful for when they are facing away from you and decide to shoot anyways, and Rainbow Experience is super important to me as I find it makes it much easier to see Experience Orbs. No Stance Transition is again a massive feature for accessibility and makes it much easier for me to play the game, as without it I can get disoriented very easily. The alternative Absorption sound is excellent for "readability" of the game, as it can be difficult to pay attention to health bars and several mobs at once, and Bubble Columns popping makes it much easier for me to actually tell where they are, especially in large bodies of water. Silverfish step sounds make it much easier to tell if danger is near, especially early game, and Channeling II allows the enchantment to have use much more often.