Foreword

Hi there ! Sorry for the incoming long and intrusive post, but since I don't know where the Aether II artistic direction is going and since I've find someone here who also want to improve the Aether in a more "classic" way through this addon, I can't wait to see new things coming in, but I don't know if raptor4694 (praised Dev) has a ToDo list, is already working on something or whatever.
I'm just doing this to classify all the ideas that came to me, and I'll make it as a kind of ToDo/ToNotDo interactive list : instead of creating a new issue, you can post your suggestions in a comment below and I'll come frequently to edit this post. That way, raptor will not have to browse much.
Before posting new suggestions, make sure to have a look on this list :

Features approved by the Dev will be written like this.
Those rejected will appear like that.

(If you're not okay with this concept, raptor, I'll delete this foreword and only keep the list of suggestions below.)

New suggestions

Here are listed the suggestions I've found in comments and waiting for raptor's judgement :
Nothing yet

Suggestion List

Note : some of the ideas listed below are inspired by the work of GuildedGames on the Aether II. I'll state it when it's the case and am aware that adding a part of THEIR work in this addon will require their permission. I didn't put suggestions as 'Changing X texture for the Aether II's one' myself because it can be done individually with ressource packs and cause such modifications should officially occur only if it's really needed to enhance the addon.

Blocks

• B1. Add new Wood essences for Crystal, Holiday (and why not Golden Oak) Trees (saw the Candy Cane Block in Aether II, had no clue of its origin/purpose but immediately thought a Candy Cane Wood would nicely fit in a Holiday Tree)
• B2. Add Holiday Tree Sappling (Crystal Tree Sappling can already be implemented thanks to Aether Lost Content, and maybe they will complete this point as well)
• B3. Add new Flowers in the Aether (and not those from Vanilla) (Aether II has added new ones and it could make the place a bit more colorfull)
• B4. Add the new Aerclouds from Aether II, but beware : their Golden Aercloud drags you down. We should keep our classic Golden Aercloud and add an Orange one which drags you down. The Purple ones can't appear naturally and are made by enchanting Green ones (in the Aether's Enchanter, of course)
• B5. Add Icing Sugar as the Aether's Snow (should be edible, but not without more ingredients).
• B6. Add the Confisery, a device which allows us to make Treats (2x2 crafting space fuelled with Swet (or Icing Sugar))
• B7. Add Emerald Ore (see M1) (adding Redstone Ore can also become an option, but seem pointless if I have no idea for Aether Redstone devices)
• B8. Add new Crops (I'm still searching which ones and what food they could make. Edit : why not Cinnamon Reed to make Ginger Dough (or directly Bread) (then used in B6) ?)
• B9. Modify the Sun Altar GUI with a Pause/Resume button to make the time stop and have an eternal day/night on demand (maybe add symbols above or below the Select Time to have a better idea of the time selected).
• B10. Change Skyroot and Zanite Doors and Trapdoors textures : for now they are just swap colors, but each Wood essence should have its very own design.
• B11. Change the Skyroot Log texture so the inside color correspond to the Planks obtained.
• B12. Correct other aestetic problems like the 2 previous points because Guilded Games might not do it to keep the mod "as close to the original as possible". To sum it up : Slabs are all named "tile.null.name", the Incubator spread flames particles up to 4 blocks above itself, Holiday Leaves are opaque (even in Fancy), the side of the Aether Grass don't become snowy when it should and, in my opinion, the Enchanter should be orientable with 1 front (instead of the 4 it has currently) and have a special texture while emitting light when it's cooking (like regular Furnaces) (the Incubator should have a "On" texture as well, and why not a external display of the Egg being incubated ?)

Items

• I1. Add a "Dungeon Finder" (with a better name than that) for each kind of Dungeon (go with M1 and E1). It would basicly work like an Ender Eye (i.e. with a chance to be lost after 1 use) to show you the nearest Boss of the corresponding tier (not the nearest Dungeon : it may lead us to an empty Structure).
• I2. Add new Foods : new Meats for all the passive mobs of the Aether (even Flying Cows and Phygs which currently drop Vanilla meats), new Fruits and new Treats (Aether II did all of this, so why not). The Meats should follow the original idea of raptor : they have to be enchanted AND cooked to become edible. Besides, I still have no clue of how a Furnace can work in the Aether while Fire and Lava are prohibited, maybe this will need a fix (the fuel is not a problem : we can make Charcoal).
• I3. Add the new Parachutes from Aether II (their Golden become our Orange, as in B4). Modify the Green so using it makes us fall as a leaf : the direction taken while falling change randomly every 2 seconds.

Mobs

• M1. Add Pilgrims as Aether NPCs, with jobs such as Moa Raiser, Confectioner (related to Treats, see B6), Slider/Queen Valkyrie/Sun Spirit/King Aerwhale Adept (sells I1 among other things). Their villages can be generated either on islands, or on clouds, or as floating houses with ballons or (fake) propellers.
• M2. Add Easter Hare (neutral) which can drop Chocolate Egg (can be eaten like that for 1 Food Points (/20), also useful in B6).
• M3. Change the Flying Cow so we can get Nectar when milking her (the idea is that each Cow species in Minecraft gives a different "milk"). Will not remove Buffs and Debuffs like usual Milk, but gives 2 Food points and Saturation Buff for 5 seconds (may be useful in B6).
• M4. Don't kill me for this one, but I think the Phyg needs a new look : currently, he just looks like a regular Pig with overly huge wings. I made a try for making him look like a boar with smaller wings, but their textures aren't mirrored correctly : one of the wing is upside-down. So can we pretty please at least redo the Phyg model so I can give them smaller wings with good mirrored textures (the model of the Flying Cow should be redone as well if there are people who want to give them smaller wings too) ?
  
  I really only changed the textures on the image above : the model of the Phyg is still the original here.
• M5. Add new colors for Moas (if we already can change a Moa's color, ignore this point : I'm an ignorant). EDIT : I just found the mod Extra Moas which add new colors AND new abilities. I didn't speak about new abilities at first but it seems obvious now that it should automatically go with the new colors.

Environment

• E1. Change the spawn rate of the Dungeons (I think we can too quickly find a lot of Silver, Gold and Platinum Dungeons after entering the Aether) (go with I1)
• E2. Add new Biomes like Sweets Toundra (cold biome, Holydays Trees and Easter Hare only appear there) and Irradiated Desert (warm biome, saw some Irradiated Stuff in Aether II, have no clue of their origin/purpose but gave me the idea of this for-now-empty biome). The current Aether Biome should be renamed as Skyward Forest.
• E3. Add Giant Jack, a huge bean-like Tree either generated as a simple Tree (mainly (or even only) in Skyward Forest) or as a Structure with a castle on its top (in that case, it would appear isolated, as Crystal Trees are) (Saplings don't generate the castle, only the Tree). Has obviously its own Wood essence (the raw Wood can be climbed like if Vines or Ladder were on it)
• E4. Add Ginger Bread House where you can naturaly find B6, and why not a kind of Witch (or a Confectioner Pilgrim). This Structure is mainly made of Ginger Bread Blocks (can be confectioned with B6) and would appear only in Sweets Toundra.

Mod is dead.