The trouble with this term is that it kind of has an all-stars vibe to it; there is an implication that each of the aforementioned fellows is already a world famous virtuoso in his own right, and their combining of talents is the kind of earth-shattering event foretold in Sumatran prophecies and heralded by the death of planets.
Which is almost bang on, except that pretty much no-one has ever heard of the bands that these guys usually play in (Converge, The Hope Conspiracy and Bloodhorse). So supergroup perhaps isn't quite right...
But mundanegroup makes them sound kinda boring, splendidgroup sounds sarcastic and prettycoolgroup is a bit non-committal.
I'm going to go with fuckingsavagefacepeelinghardcoremergeforthekillgroup.