Autonomous_Soviet_Socialist_Republics (ASSRs) belong to Soviet Republics (SSRs). There is no precedent that I know of that an ASSR would be a top-level entity within USSR. And indeed the historical Crimean ASSR was within the Ukrainian SSR.
So what they've voted in is becoming an ASSR within Ukrainian SSR, which turned into the Autonomous Republic of Crimea inside Ukraine.
I don't see any way there to treat Crimea as ASSR inside Russian Soviet Federative Socialist Republic (RSFSR, e.g. Russia). I also don't see any ASSRs becoming independent states, even though one of the latest USSR decreesone of the USSR decrees would permit it.