If I read this article correctly …
Well, first, begone “One D&D”! Welcome “D&D 2024”! The concept is, I think, kind of the same, but now they are adding a year on there so that it will sound out of date at some point.
The new core books will be … a thousand pages long? Crikey.
The reason for that length? All the old stuff (“D&D 2014”) will still be in there, alongside the new stuff (“D&D 2024”). You don’t have to choose! You can mix and match and blend and use it all, because it will all be backwards compatible, in all directions! Fun for all, especially the GM (who has to keep all these things in mind) and various software systems that have to keep track of double the rules and selected options.
WotC is trying to have it both ways: a new system to be excited about (and to buy books for), but not obsoleting the old stuff (though you’ll really want the new stuff because some players will want the new stuff). So all that money you invested in D&D 2014 stuff is still a good investment, except that you’ll want to buy the 1000-page core books for the new version because that’s what all the cool kids will be doing.
I’m fine with their sticking with the basic 5e mechanics, which are sound. But the forward-backward compatibility stuff is dodgy. I still would rather they just call it 6e or 5.5e and be honest about it.