Verb agreement in "Where is the Messiah and his Kingdom?"

Formal agreement requires are. Those who argue for is will see 'the Messiah and his Kingdom' as a unitary concept, thus allowing notional agreement by means of the singular.

It seems to me you could reasonably use "is" if you have a comma after "Messiah". So if we allow discarding a comma (which imho isn't exactly vital), it's just valid elision from...

"Where is the Messiah and [where is] his Kingdom?"

FWIW, I just Googled "where are the queen and her" (1 result), and "where is the queen and her" (3 results). Not much to go on, but it does suggest the singular verb form isn't that ridiculous.