I still have my Volo's Guide available in Beyond, I can still even add the monsters to encounters and I think I can build something like a Tabaxi using the Volo's (legacy) rules instead of the Mord's newer rules.
What I am talking about is a shift in usability on Beyond. When the 2024 books first hit, the 2014 books will be made Legacy content, but I expect I will still be able to build characters using the 2014 versions of the classes. At some point later in the year, I expect the 2024 sales to slow at a point that Wizards tries to pull being able to build characters with the 2014 rules (instead of the 2024 rules) to push 2024 sales, and that they get pushback from the community to keep the ability to build PCs with 2014 options - if you bought said books before 2024.
Not a scandal, just disgruntlement - Grognards: "we want our old stuff to keep working", WotC: "Buy our new stuff!".
<EDIT> Oh, I see I stated the 2014 actually vanishing off Beyond as well. If v2024 tanks badly enough I could see that occurring as a reactionary measure to try and push the new books, so I figured I'd put it in as a "worst case scenario". But it'd be a slimy, desperate and dumb move that'd get a lot of grief. Something right up a crappy money-grubbing corporation would do. We'll see if WotC/Hasbro gets that desperate (cough continued poor earning for Hasbro cough).