The fact that there are known issues doesn't mean that finding new, unknown issues will slow down the work on the known; it's up to the team to decide what sort and what amount of feedback they'll be able/need to process (and to adjust if they were wrong).
Gradually enabling a feature is not an "experiment" on some poor victims, it's a normal development strategy (as opposed to sudden revolutions/waterfalls on the wikis). I still don't see any indication of why it should raise the end net harm of the VE development on the wikis.
I don't know how to enable the preference at some point of users' lifecycle; probably, in the same way you do it for half new users. A hook I assume, it was mentioned in some Echo and enotif bugs.
Nemo