John Kirkpatrick's band Umps and Dumps (years ago) had JK on C/G anglo concertina and Tufty Swift (sadly deceased now) on 1 row C melodeon. They played everything in C.

I always thought it would be fun to have a band like that and include a viola as it could play exactly like a fiddle in G. Despite some potential opportunities, I never got anything like that off the ground.

Of course, taking an oufit like that to a session would be a bit antisocial, though I do know at least one D/G melodeon player who likes the challenge of playing in C...

Anahata