Just like they've done for Species options?
Again, look at the Aasimar, you have the DMG version, the DMG + Tasha's Version, The Volo's Version, the Volo's+Tasha's Version, And the Multiverse option. All useable, all competing... and no issues. No confusion that has been palpable in the community. Heck, we currently have the Deep Gnome as a subrace in Mordenkainen's and SCAG... but it's own racial option and not a subrace in Multiverse. And again... no confusion.
Feats? Feats have been revised before, edited, so what's the problem?
Spells? Same thing. We've had errata'd spells.
What you are referencing
can be confusing but the examples you are referencing are so small that it doesn't become a larger problem. Having different versions of Deep Gnomes matters less than having two different versions of the Warlock built around two different ideas, or having a Druid that has Wildshape that is meant to be balanced while keeping the flawed older version. You're trying to pick away by picking small example of the coexistence of different versions of something (which, hey, I don't like
anyways) when we are talking about doing an entire rework of feats, backgrounds, race/species, classes, and even some equipment. That's not at all on the same scale, especially when the latter is all part of a single unified push. Having a few different versions of Aasimar or Deep Gnome is not completely revising the 12 standard classes along with most things that go into character building.
But you also reference "errata", "revised", "edited"... in these cases, those are meant to
replace something, not coexist with it. Something is
changed. Now you might not
know about the change, but the intent by the Devs is still there that the new is standard and the old is gone. What you are talking about with 1D&D is not errata, but rather an addition. And that's just bad design, in my opinion.
Okay? But that is a completely different issue. That is a homebrew issue. That is "we don't want to play with these rules, we want those rules" and that is a choice. And if you declared that doing so was illegal, so say Wizards of the Coast.... they'd do it anyways.
No, that's not a homebrew issue. When the devs make the conscious choice to make two sets of classes available to your players as standard (which is the case), that's different than letting someone play with an Unearthed Arcana class. That's a design choice, and I shouldn't have to homebrew out the stuff they were basically meant to be errata-ing out with these new classes.
The whole point with the new classes is to fix balance. Even the arguments about adoption are largely based around the idea that the vast, vast majority of people are going to convert wholly to 2024 and not use 2014... so why even have the option? Why not make
that the homebrew choice, to bring in old classes rather than to have it the standard?