TerraDave
5ever, or until 2024
Not only that, but being able to play a newPHB Ranger with a Tasha’s or whatever subclass. Being able to take fears from any official 5e D&D book regardless of which PHB you built the character from.
I can't decide how hard it will be to be compatible with the supplements, or how much that limits changing the core books.
The ranger is such a special case that it can have its own treatment. But, if, say, the new PHB rogue has some long-rest recharge abilities, but most rogue archetypes in Tasha's or Xanathar's doesn't, does this matter?
And at some point, they will want to supplement the supplements. Maybe many years from now, or maybe sooner. But it will come up. With the monster books they are already doing it, before releasing the new core books.