Uni-the-Unicorn!
Hero
Love the idea, but don’t think it will happen. I would like to take it even further and have certain rules / mechanics tied, at least initially, to certain settings.The Magic The Gathering settings belong to D&D like any other setting, including Eberron and Ravenloft, and homebrew.
Indeed, for the sake of homebrew, I want the core rules to be a setting agnostic as possible.
Ideally, the Forgotten Realms setting becomes a core rulebook that is separate from the Players Handbook.
The Players Handbook can have the Human race only, with a note that the DM can include one or more other races as well. The only default setting is popular notions of "medievalesque" and magic exists.
Then the Forgotten Realms Guide has a freedom to detail the beloved D&D races like Elf, Tiefling, and Dragonborn, in ways appropriate within the narrative context of Forgotten Realms and the multiverse that is peculariar to it.
What happens in Forgotten Realms, stays in Forgotten Realms. Unless a DM wants to import something from there into a separate setting. Samething for what happens in a Magic the Gathering setting.
I could make the core books smaller and provide modularity through setting books.