The Dead played a billion covers. Some they played forever: Me & My Uncle, NFA; some just the once: How Sweet it Is (from the DP 30 Academy of Music shows that I’m always honking on about). Some songs, though: it’s better the Dead never sat down to figure out the changes.
Dubstep would not have worked; Phil would probably like it. If you haven’t heard dubstep, it’s the sound of a Transformer getting raped. Actually, Mickey might have liked it, too. This is what dubstep is: it get interesting 90 seconds in. I understand why half-naked teens on drugs would love dancefucking to this, but it’s not for listening.
Itsy-Bitsy Teeny Weeny Yellow Polka Dot Bikini (fuck you all for making me type that) would be a poor choice as Bobby would fuck up the chorus so badly that everyone would think it was a Dylan tune.
Any of the particularly tricky Rush tunes: La Villa, YYZ, By-Tor (not the Snow Dog, oddly enough.) The Dead had the chops to pull it off, but those tunes required precision and practice. Even the Dead’s more complicated tunes, like Terrapin–if you missed the musical turn, you could wait for it to come back around again. Plus, there were twice as many people in the Dead as Rush, man.
Devo. Any deconstruction-type stuff. The Dead did not dismantle, in fact they piled on, always. They were rococo and baroque. Also, broke, but that’s for a different post.