Yeah, I'd love to see Maestro vs. Old King Thor. It would be an epic battle, that is for certain. And I would love to see it end in a manner similar to all of their battles: A virtual stalemate.
Of course, I can imagine Maestro saying this to Old King Thor:
"You're not the only one who has grown more powerful with age, Thor, for as you can see I'm still the Strongest one there is!"