As far as the lack of mechanical additions goes, I'd like to remind that for D:OS2 Larian have held back on adding the Summoning/Polymorph skillsets and the entire crafting mechanic up until the later half of EA, which lasted only 1 year in that game's case. And since there are supposed changes to the reaction system coming in, and many unimplemented spells which are there in the code but aren't available without modding yet, it's safe to say that there are still alterations to mechanics to be expected.
At the very least, we are getting difficulty settings. Maybe wizards will be allowed to scribe non-spellbook scrolls only on the lower ones... not that they should be able to do that at all, but if multiclassing makes it into the release (which I am positive it does, it's less about implementation - although, judging by Owlcat's example, you can get all sorts of total level-related bugs if you don't know what the hell you are doing - and more about balancing), then having wizards just have access to every spell in the game, including cantrips which they can somehow scribe too, would eliminate any purpose for mixing spellcasting classes in the first place.
