Pretty much what
Count Bleck is all. We know for a fact Zoroark is in from the very first trailers but that's about it.
From pure commercial standpoint (despite GF/TPCI's inability to do PR properly...), it's very likely that all Hisuian forms will be available in the game, not necessarly native but at very least transferable. It'd make sense as well as being an incentive for people to buy LA if they haven't yet, to be able to use their (figuratively) shiny new Enamorous or NotWeavile in VGC 2023.
Also, if we want to use SwSh and Let's Go as "regular pokemon games with dexit" precedent (I won't include BDSP due to them attempting to be a "faithful remake TM") the presence of a given pokemon in the regional dex who also has a regional form will also imply the presence of all its other regional forms / evolutions.
SwSh for example had coded in all the regional forms of galarian forms present in the dex as well as Alolan forms of kantonian pokemon and even (Alolan) Persian / Cofagrigius, though some of them were only legally obtainable once Home compatibility was released.
Let's Go had Alolan forms available both via transfer and directly in game from specific traders.
A extra case in point in SV specifically is that they already shown the presence of Kantonian Wooper on top of Pooper.
TLDR: While we have no official confirmation, there are many hints pointing at the availability of Hisuian forms in the game, at very least the ones of pokemon also present in the dex, but potentially all of them.