I feel like that sort of thing is just going to cause confusion and anger because it's basically a stealth edition change and everyone is going to recognize that the classes, spells, feats, etc... are different.
That's the real question, to which we don't know the answer. WotC are claiming that they don't want to do another edition change and that this will be backwards compatible, so that it really will be more like when
Tasha's came out rather than like when 3e or 4e came out. Their stated goal is specifically to avoid the kind of schism that you describe (yes, I am aware that this is deliciously ironic given the schism they have just created for wholly different reasons).
We don't know if what they claim to be trying to do can be done, or if they will succeed. The way I see it, there are three likely outcomes:
1. It's just a new edition and folks have to make a choice. Older texts no longer work without major adaptations. Significant disruption and jumping off point.
2. It's more like a .5 edition and folks feel less pressure to choose. Many older texts still viable, with some minor adaptations. Smaller disruption and jumping off point.
3. (WotC's stated intent) It's an updated version that works fairly seamlessly with current 5e, so that players can pick and choose what to keep and what to update. All older texts still viable, aside from a few tweaks. Minimal disruption and jumping off point.
I don't know if option 3 will actually happen, but it isn't logically impossible and I understand WotC's incentive to attempt it, so I am interested to see how this works out. I think the prevalence of DnDBeyond is a huge factor, as it gives WotC a strong incentive to make option 3 work (i.e. as the first updated book they need the new PHB to be able to work with all the other stuff on DnDBeyond).
But honestly, I think their mismanagement of the current situation has probably put all of their planning into question.
