FYI these come from the perspective of a player that desires a truly dynamic & impactful mod - one that could heavily change the game experience. I, perhaps, went a touch overboard...

I have some thoughts that follow this line of thinking, this "even the best equipped needs to respond" concept. Note these would be adjustable via configs:

Goo activation timer: After X days in-game have passed then Goo world gen will take place. This gives players time to get started, set things up, then later have to deal with potential Goo issues.

Goo mutations: Goo, either over time or via interaction with biomes/blocks/etc, can mutate into different variants. Perhaps it could be similar to Chickens...Goo A within X blocks of Goo B has Y% chance to mutate into Goo C when Resource Z is present.

Goo variants: Created either through mutations and/or world gen:

• Ore Goo: Goo that grows over world-gen ores. It could use the ore dictionary to have variables like 'only iron' or 'all Copper'. It could have a depth requirement, light level, range (only spreads to ores within X chunks), proximity to other blocks/structures/entities, etc.

  There could be a secondary mutation that makes the change permanent (remove Goo and you are left with Minecraft Stone or Gravel or whatever), or a "low quality" version is left (like the old Railcraft ores).

  This creates a situation where gathering additional resources (unless using something like a Void Miner) would become increasingly challenging thus forcing the player to expand their default playing area.

• FE/RF/EU Goo: Goo that is attracted to energy. There is X% chance that it'll spawn on a block that contains Y amount of FE. Once spawned it now has increased growth rate along all FE containing blocks. This could start consuming a players power grid along cables/generators/storage/etc.

  Typically players with high tier FE generation have a greater amount of resources available, so it could be configured to have a greater chance of mutation on blocks/entities with higher amounts of FE contained (and/or spread faster). That would be a huge change for late-game playability...a player would need to distribute their power gen over multiple networks/sources in order to prevent Goo from obliterating their ability to produce FE. That would make those earlier tier power gen/storage/transfer networks viable throughout game play.

• Goonimals: A variant of Goo that takes over mobs (in this case passive mobs...animals). Odds of generation increase with the number of animals present within a chunk (stuff too many sheep into a pen and you've got a near constant conversion of them go Goonimals). Goonimals could have X% chance of the ground beneath them turning into Terrain Goo (or other variant) and Y% chance of converting other mobs into Goonimals.

  Like the FE Goo this would force players into being more thoughtful about their animal farms vs. just cramming a ton into an area and having it be a "set and forget" situation.

  There could also be a version that spawns (as or on) hostile mobs...a Goombie (Goo Zombie) that touches and infects, a Gooeleton (Goo Skeleton) that shoots and infects, a Gooeeper (Goo Creeper) that explodes and spreads Terrain and/or Normal Goo. And those hostile mobs could be configured to passively or actively attempt to spread Goo. A Goolem (Goo Snow Golem) that spreads a trail of Terrain Goo.

• Misc Variants of Goo: Crop Goo, Water Goo, Oak Goo, Dirt/Stone/Diorite/Gravel/etc Goo...basically block specific Goo that could exist to either be a source of mutation (and passive) but part of world gen (X% of Sand generated is Sand Goo) and/or be active (spread to other blocks/entities without mutation). Could be biome specific (Sand Goo only is part of world gen in 'hot' biomes, Gravel Goo only in Mountain biomes, etc).

  That would also give the sort of "timer" effect for players...left alone for too long and it'll become something difficult to deal with.

Goo Infested Blocks: Like vanilla 'Infested Stone' there could be stone (and/or granite, gravel, sand, etc) that's visually normal but infested with Goo. Mine it and there's a Goo Event - rapid generation of Goo around the player, or a forced mutation of nearby Goo, or their mining tool/themselves/random inventory item/armor/etc becomes Goo Saturated and needs to be cleaned to prevent contaminating other blocks with Goo (perhaps visibly or not...and if not a Goo Alarm trinket would indicate the presence of Goo Saturation and/or highlight nearby Goo Infested Blocks). If Goo Saturation is a permanent effect then this would force players to use a variety of tools vs. a "set and forget" situation.

Day/Night growth: Goo only spreads during the day or night (when player can sleep or not). Goo only can spread in light level X. Only when it rains. Increases growth in rain. Etc. This could discourage players to sleep or encourage the desire for rain ;)

Goo Safe Biomes: Some biomes (by "climate" or "category") are Goo resistant...Goo won't spread and/or mutate in those biomes (or spread/mutation % chance is decreased). Encourages players to set up in specific biomes.

"Naturally" Goo Safe Blocks: Some naturally generating blocks, say Mossy Cobblestone, are naturally resistant to Goo...this could be the block itself or a small area around the block (1-2 block radius). Good for very early game Goo mitigation.

Sound reactivity: Goo has X% chance increase (or decrease) of generation/spread/mutation when sound conditions are met. Have a base with a lot of machines in close proximity = more potential for Goo problems, so spread out your facilities. Or it's attracted by the sound of an active Nether Portal.