According to this MTV piece, Koei will release Fatal Inertia EX as a PSN exclusive in late May.
It's going to cost $30 in the US and will never be sold on disc.
“After the launch of the Xbox 360 version, we had a unique situation that allowed us to reflect on what could be done with the PlayStation 3 version,” said lead producer Mike Bond. “But having watched the growth of the PlayStation Network’s user base and the game’s multiplayer component, we felt the strength of this game would be in its online community.”
More through the link.