As for the central question of full-length Myriad novels, probably not. The "mirror universe" has it's place in accepted continuity, the "myriad universes" do not.
If by "accepted continuity" you mean screen canon, there's one that does: The Chimes at Midnight is in the same alternate timeline seen in "Yesteryear." Also, Places of Exile does tie into events from canonical continuity and features one character who did appear in a televised episode -- the same actual character, not an alternate version thereof.
Anyway, why would doing MyrU as 80,000- or 100,000-word novels be fundamentally less acceptable than doing it as 50,000-word novels? And what has "accepted continuity" got to do with it?