Henadic Theologian
Legend
I would bet for Mystara, but don't hope more one sourcebook.
The new worlds form MtG seem to be designed to be adapted as future D&D settings, even Duskmourn, the haunted-mansion plane.
Today WotC would rather to sell crunch, because players don't need spend money to get fluff, lore or background thanks fandom wikis.
They have not done a MtG setting since Strixhaven, which did not do well.
They did minor monster D&D Beyond product for Eldraine, but it doesn't even count as the setting for dmsguild. A mention for Tarkir and Kaldheim each in Fizbans and Bigybys respectively.
Ask yourself why?
Its because MtG setting crossovers no longer fit their goals going forward. Maybe they make an exception for Tarkir.
No with rare exceptions, like Tarkir, products going forward will be for classic settings and D&D version of Universes Beyond (Think Diablo, Zelda, Bayonetta, Lodoss War, Marvel, etc...?