in fact there are so many mecha shows around, it would be hard to choose. Armageddon2089, would allow MGP to do a game without having to worry to much on the legal side as it is theres. However the problem is not many people know of it.
hence the use of an anime or american mech orientated game would fit the bill, as people will be able to attach to the background, take SST and ACTA for example's.
personelly I think Robotech / Macross would suit better towards the ACTA / VAS side of gaming while other shows lean more to the Evo side.
Full metal Panic would be brilliant as an evo game, its heavily mech based however the line combat forces still use tanks and infantry, the two sides of warfare compliment each other, you could have all sorts of adv rules, like the ECS invisible mode, Lambda driver, AS pilots foot slogging it, then there would be RAH-66's with the Mithril side, Hinds and apache's or whatever for everyone else, infact mongoose will have allready made most of the regular military forces allready with BF:Evo.
Actually I think starting tomorrow i'll start a FMP mod, just how do you deal with armour on a Mech?