Shrinking worlds would be great, but it needs to come with another change: lifespans. Coaching for 140+ seasons at a school is ridiculous. After your coach reaches 50 seasons coached (which means he is north of 75 years of age), he "retires", you get a new coach, and you're back in D3.
Implement this change, and when coaches retire, their new career starts on a world that we identify as a "keeper", versus worlds that will shrunk, where new players can't join; the shrunk worlds just age out over time.
Then, re-introduce injuries, where tired players are at a higher likelihood of getting injured, with their injuries more severe, and make stamina and durability relative statistics again.
These three changes would address most of what is fundamentally wrong right now with GD: ghost towns, powerhouse teams that impact competitiveness, and a lack of dynamism outside of basic RNG.