This would be fun as long as they add farmers with weapons, police, military, then the Kiryu-Kai in this order so you're going against some kind of weak to strong resistance in the early game before you run across the X-COM forces. The gangs you can entice to join you so they can do evil for you in some cases. Alien infiltration will be fun if you add some kind of Agent system with the model of other popular games.
Oh yeah, this would be awesome.
I love this idea if done correctly, because of how much freedom you will have to do anything you want. You just point anywhere in the map you want to go, to do any mission you want, depending on the resources you have, depending on how many alien forces Mars will send to you. The mother brain will evaluate how you're doing every alien month of the alien year. Have strange names for months and change everything for immersion sake.
Game obviously starts even before the Kiryu-Kai.
Many countries initially attempted to deal independently with the aliens. In August 1998, Japan established an anti-alien combat force; the Kiryu-Kai. Equipped with Japanese-made fighter aircraft, the Kiryu-Kai certainly looked like a powerful force. However, after 5 months of expensive operations they had yet to intercept their first UFO. The lesson was clear: this was a worldwide problem which could not be dealt with by individual countries.
