[Either [Latin] [Cyrillic]] is a very simply type taking advantage that the language only switches at word boundary.

Huh. That doesn't quite address my objection (CamelCase like EnglishEtРу́сская still un-works), but that's actually a good point in the overwhelming majority of cases. I'm not quite convinced this approach works in practice (I'm sticking with "A"="A"="A"), but I'd definitely like to see a more technically fleshed-out design.