It's been a while since we had a fantasy band thread here, so I'm starting one. To continue my life pattern, let's start off in the lamest of ways with a fusion/prog supergroup.
Guitars: Allan Holdsworth
Guitars/vocals: Adrian Belew
Drums: Gavin Harrison
Bass: Jaco
The band would release one amazing album and then Jaco's bullshit would dissolve it before the second hits, rumors of how amazing it was going to be will outlive anyone in the band.
Or for metal:
Drums:Bill Rymer (Dillinger Escape Plan)
Guitar: Tosin Abasi
Guitar: Fredrik Thordendal
Bass: Where were going we don't need any bass.
The hype of their first album will never live up to the product and they'll go back to their respective projects shortly thereafter.