The special syntactic form doesn't bother me that much.  '**dict' is already a syntax error in many places, but allowed in a few other places.

I also do not think the purpose served is important enough to warrant a new special form.  The actual same conciseness can be achieved with a function that does just a little bit of magic, e.g.:

    func(**Q(u, v))

Someone linked to a library that apparently does the magic a bit better than my 5-minute version (which required quoting the variable names).  I think it was you who complained that sys._getframe() might be CPython specific, which is true.  But probably other implementations could do different magic to make their own Q(), so that seems of little importance.

I really doubt I'll ever use a magic function like Q()... but the fact that I could have done so for the entire 20+ years that I've used Python tends to emphasize that the need isn't REALLY that huge.  And if the need isn't large, reserving new syntax for it isn't compelling.