Urriak Uruk
Gaming is fun, and fun is for everyone
Tarkir has more setting meat then Kamigawa but it shares two problems, one it to is over shadowed by Kara Tur, and secondly WotC wants a new MtG Asian themed setting, not the old ones, plus Tarkir has that weird 2 time line issue. I don't think they are going back to Kamigawa or Tarkir in mtg, never mind D&D.
Here here are the MtG settings I see getting D&D setting books.
Theros is already getting one, but future AP is possible.
Ravnica already has one, future full AP is possible.
Zendikar
Dominaria
Amonkhet
Ixalan
Lorwyn
Eldraine (after it gets a second card set)
Ikoria (after it gets a second card set)
I don't see the rest happening for various reasons.
No offense, but I'm pretty sure Wizards would take Tarkir over Kara-tur. I don't think Kara-tur has gotten it's own product since what, 1988? I'm not sure Wizard's is willing to update a setting by white guys 30 years ago if they have a setting that was released a lot earlier and is a lot less stereotypical Asian fantasy.
That said, I don't think they're mutually exclusive. But if they were, WotC would pick Tarkir for a book hands down.