Oh theres so many good directions for that to go. Super thin leggy ones that can barely walk. Long weiner fluffies. Someone has already done huge wings (i think they called it true pegasus?) but giant horns that slice up their mothers in the womb. Alicorns with both of those.
If i had money i’d comission someone to make a breeders magazine of these.
Okay, I need more wild fluffy content instantly.
I have 5 parts about wild fluffies on my page 
Im imagining the scene that would be created by breeding a fluffy with a jellenheimer. xD “Ou wan fwuffy do wha wif dis??!”
My guess is that it’s the same issue that opossums have, where the harsh environment kind of curbed their lifespan.
Essentially, since the average opossum is gonna be dead by 1 or even 2 years old, there’s no real reason for ‘longevity’ to be an important trait to develop. The genes exist, but one with ‘live longer’ genes isn’t gonna be any more successful than one without them when they’re both run over by a car.