Leaving aside the comments on breaking changes, I disagree on the concept of this idea.
A player can use 3 labs from RCL 6, which means with the simplest of manual market interaction, a player can be making and applying T1 boosts as they also gain access to the extractor at this RCL.
If the spawn applied boosts, how would it work? Does the player need to remove the boost they have made from a lab, and move it into a spawn? The spawning method then gains a new parameter stating how much boost should be used? This sounds like more complexity, not less.
- What interaction would this have with renewing creeps? How would I be able to spawn (say) an attack force, have them all renew to the same TTL, and then boost?
- This will add more complexity regarding spawn locations, as a creep will need to be spawned in a spawn that has the correct boosts.
- How many boosts, and how much of each can a spawn store? A creep can be using many types of boost at once, after all.
Even if I agreed with your idea, it is insufficiently detailed.