some objectives could be for example, similar to conquest as it is but with fortified bases, and each time you cap one its permanent. so you would have 2 rounds. one round you would defend the other round you would assault.
making the bases actually destroyable and cap-able only once would really up the anti.
another type could be similar to first but instead of bases you must escort something to a destination then rendesvous with something else. this would mean that essentially you would just have "moving" bases that you must escourt then guard.
the aim being to go as far as possible before the time runs out (you would achieve your objective) or your escourt fails. then in the second round the roles would reverse.
technically if a game were long enough a player could be given the option to use the cbills earned in said game to buy items at a discount price, so for example if you made 500,000cbills playing a 30 minute game you be offered a salvaged engine or weapon for 250,000cbills.
this kind of game would would also allow for the introduction of real salvage which is in essence getting free weapons and stuff from mechs you have slaughtered on the battlefield which is why so many people love salvage

anyway these are just a couple of ideas allowing for players who want to play long games can do it without sacrifising their xp/cbill gain what do you guys think?