I am conflicted about full on moveset wipes. On one hand, there is so much fun history attached to movesets. Random event moves like Octazooka Sableye and bizarre footnotes in movepools like Water Gun Donphan are super cool to have around. Seeing everything finally get wiped away is a bit sad. It's also just a bit annoying knowing stuff you set up for future use like teaching your Arceus all the tutor moves in PLA is just, you know, not a thing anywhere.
That said, I realize programming robust movepool legality checks is a bit of a challenge and it's a lot easier to just collectively clean things up so you're only tethered to one game. It also generally is just kind of wild that we can send Pokemon back in time again, now that they have no reservations lopping off a bunch of a Pokemon's data to store it server side.
Also, given that intergenerational Gen 8 stuff preserves a Pokemon's ribbons, EVs, ability, etc, there's a solid chance that if this rumor is true, SWSH would have genuine tradeback Pokemon! It wouldn't involve movepools at all, but Gen 9's ability to uninvert the ability patch means a few legality issues in Gen 8 are now totally legal. Off the top of my head, the most interesting one is probably Curse + Technician Scizor, since being a VC Pokemon requires an HA. Another vaguely interesting one is Clefable; it's on the datamined list of eventually returning Pokemon, which would make the combination of Knock Off (Gen 7 Tutor) + Teleport (Gen 1 VC) + Magic Guard (Incompatible with Gen 1 VC moves) legal on it. Of course, if that system works and Gen 9 adds in the Machamp line, after a long 7 years of waiting, No Guard Fissure Machamp finally gets to reign! ...Over tradebacks Gen 8 AG I guess lol?