BattleTech / BattleForce
Would people be interested in a BattleForce 2 campaign? It takes the BattleTech rules, abstracts them and allows relatively quick and easy play with large (8+) numbers of 'Mechs. The system itself is fairly straight forward and easy to explain if you don't have a copy of the rules, which can be acquired online for about 5 bucks anyway.
The campaign could cover struggles internal to the inner sphere, conflicts between or the clan invasion itself. The system is compatible with the normal BattleTech system as well as the RPG, so a mercenary focused campaign would also work.