AOSP is used in many contexts like embedded devices where somehow enshackling it would screw up Google's self-interest in other market areas (like ensuring there is a wider population of Android developers).
But regardless, thirdparty ROMs will continue to exist regardless of how much effort it takes because the demand exists and will not merely dissipate.
How long until AOSP deviates so much from features in 3rd party ROMs that it becomes infeasible to for amateur developers to maintain them?
AOSP is used in many contexts like embedded devices where somehow enshackling it would screw up Google's self-interest in other market areas (like ensuring there is a wider population of Android developers).
But regardless, thirdparty ROMs will continue to exist regardless of how much effort it takes because the demand exists and will not merely dissipate.