Yeah Tobi from Edguy and good ol' Kiske would be great. And i have to agree that some DT stuff thrown in would be damned cool but rather more unlikely than the other suggestions i'd think...
What happened to Michael playing the Tuba for PQ? Was it all just a lie? How could you? Make it so
I hate to be a generic bastard however the two best guys for the collaboration jobs would have to be Tobi and Kai. I can't think of two greater musicians in the power metal or metal scene that would do a superlative job and mesh with the Power Quest style as it currently stands.
I met Kai Hansen this year when Gamma Ray came to Sydney, it was the best concert ever. He was such a nice dude