It probably never occurred to Khrushchev that the Soviet Union would ever collapse in two centuries, much less two generations, so it was a paper transfer, the equivalent of moving my leftovers from the kitchen fridge to the game room fridge.
Bingo! I think you nailed it.
Russification of the peoples the Tsar conquered had been in full flow since the 1880s. Thus abated a bit during the first decade of the USSR but then resumed.
If the USSR hadn’t broken up then by now the Ukrainian language like Belarusian, would have become like Welsh.
In fact, as I have pointed out before, before 2014 the Ukrainians I met in Poland were pretty meh about Ukrainian identity. This changed slightly with Putin’s first invasion in 2014, but when Putin invaded Ukraine in 2022, that really cemented Ukrainian identity.
If Putin had just used soft power then, conceivably by 2040 Ukraine would have merged with Russia.