VIC20 Core would be nice although I think a 264 Core would be more appreciated.
First the user base is greater and second: many TEDs and CPUs of that series are quickly dying recently (due to bad manufacturing/changing production methods?).
Anyway: the MEGA65 is first of all a c65 'XT' (eXtendet Technology [and in 30 years from now someone would introduce the MEGA64 AT Advanced Technology :-)]) with hopefully 100% accurate c64 modus.
But it might be wise to already reserve extensions for the 'GO' command, so it could handle GO 20 (VIC) and GO 16 (264) ;-)