I haven't really kept up with the Front Mission series after the third one, but that may soon change as it looks like Square Enix is planning to bring a new Front Mission game to North America.
The company has recently registered a trademark for "Front Mission Evolved" with the US Patent and Trademark Office. The trademark was filed on the 8th, so it could still take a while until we learn anything official about this game.
Not sure too if it's an actual new game or another rehash of an earlier release. Only three games (FM1, 3, and 4) got released outside Japan, so Square Enix has a lot of choices if it's a rehash.
The "Evolved" part also makes me think of Front Mission: Online. A PSN and XBLA release, maybe? There was also a rumor about an Xbox 360 Front Mission game a while back, so this could be it.