I think it'll be a while before we feel any real impact. I mean, first off the 3D VTT has to actually arrive - that's probably at least six months before we even get a semi-open beta, maybe a year or more. Then it'll have to properly release. Then we'll see.This. For so many reasons. I feel like when they designed 5e, and one of its main reasons for success, was because they designed it around a feeling, specifically, the feeling of old-school tabletop gaming. Redesigning around a virtual tabletop might change the feeling drastically. And, in fact, I do not even see how it can be done.
The big issue is that, if Cynthia Williams was correct (and we have no reason to believe otherwise), WotC have nearly 10x as many employees working on the 3D VTT as on the actual D&D team, which means they likely have close to 10x the expenditure - or more - too (unless the D&D team are on much higher salaries than one expects). Thus the 3D VTT represents a vastly larger commitment of resources, and larger perceived risk than TT D&D.
So then are two potentially big D&D-influencing outcomes:
1) If the 3D VTT is a big flop on full release or rapidly drops off, subscriber and microtransactor-wise, and looks like a bad investment, and WotC decides that investing further in it is throwing good money after bad, there will be an impetus with WotC to find a way to recoup some of those losses. One of the possible ways will be to sell off the D&D IP, including the 3D VTT. As the IP is reasonably popular, WotC might be able to ask a pretty large amount of money for this, likely from a videogame company. Top contender probably Microsoft because of Hasbro/WotC's close connections with Microsoft (as much, perhaps the majority of the upper management is ex-MS), but Sony, Ubisoft, EA and others would likely also be possibilities. To be clear, this isn't a certainty. WotC may well decide cutting their losses makes sense but that the D&D IP is too valuable to sell. In which case 5E 2024 version will likely just carry on, with WotC focusing instead on trying to get more games like BG3 to exist (a probably fruitless task).
2) If the 3D VTT is fairly successful or better, it will very rapidly eclipse TT D&D in terms of profitability, given the approach to monetization that WotC have already described. This means that TT D&D will naturally become a secondary concern. Not ignored, I'm sure, after all the 3D VTT still will have it's raison d'etre be fundamentally as a VTT. Initially at least. We've heard recently that WotC are trying to focus on making it as easy as possible for DMs, and almost automated, which I think will likely gradually drift the 3D VTT more towards being a kind of multiplayer videogame, essentially. Anyway, videogame aspects aren't likely to impact TT D&D. But what will is the approach to selling content. If you've got a subscription-based platform and you're already going hard with microtransactions (and again, we know this is the plan - WotC have said so is the beginning - to go hard with microtransactions), then different ways of delivering content and charging for it would make sense. WotC have already put out feelers about this with surveys. We may well see a sort of balkanization of classes, subclasses, races, spells, monsters, items and so on, as WotC attempts to focus on selling them - especially classes/subclasses/races - to players. This is likely to create a situation where, relative to today, classes/subclasses/races particularly are more expensive, and not necessarily collected in books. It's possible subscription tiers will include these, of course. It's likely to change adventures too, as any new adventures will want to work as well as possible with the 3D VTT. I suspect this may involve a degree of simplification in many areas, some reduction of abstract scenes and so on.
TT D&D is probably safest if the 3D VTT enjoys a very moderate success, perhaps doing well with cosmetic microtransactions, but poorly with rules-based ones.