1- I was kinda hoping, after re-playing feros on me1, that they could re-create a complex like the exogeni building, allowing the team and enemies to be spread over 2 floors. This could make things interesting when dealing with mission objectives. Hydra and white came very close to this vision.
2-For bronze and silver, they could allow the person creating the match to determine the mission objectives. While on gold and plat, they would always be randomized.
3-When playing objectives or doing extractions, there could be the challenge of having 2 or more members standing alone in a certain point of the map. Like a switch that needs to be activated simultaneously from 2 or more different places, or having shuttles landing on different places during platinum extractions forcing the group to spread on the map, each person having a designated point of extraction. Another option would be a holding the map situation, with 2 members extracting data together.
4-They could make a prothean dig site map that played like a maze (like the deep roads in dragon age 1), with multiple paths to the same place, creating the chance and risk of ambushing and being ambushed, with some large areas and some corridors.
5-Aside from the main mission objectives, the game could offer you (beforehand or out ot the blue during the mission) some special bonus objectives, like: a-Kill a character with a tech explosion. b-trigger a kill-streak. c-Complete the assassination objective without firing a missile. d-Kill something with a heavy melee. e-remain at a certain space for x amount of time. f-prevent enemies from entering a certain zone.
The game would scan the players and request only bonus missions that the team is capable of doing. For instance, if you only have a group of biotics, the game could never ask for a tech explosion. The game could also ask for cooperation, like asking for a snipper or shotgun kill of a opponent who is being held by a geth prime heavy melee. Another example of bonus mission would be to make member A the assigned protector of member B. So whenever b went down, it would have to be member A to revive him. Of course, member B could always revive himself and be revived by any other member, but then the bonus points would be lost. Other example of bonus missions could be ask a certain biotic member of the group to not fire his gun(s) for the remainder of a wave.
Failure to fulfill the bonus objectives would not end the match. They´re just there for additional points, money, fun, challenge and to make things always different.
6-Wave 11, instead of extraction, could, as an alternative, be a classic boss fight, with a Yahg, tresher maw, a clone rachni queen, a geth colossus, a flying vehicle (Kai-lame ship or the boss fight from kasumi dlc), or a very tough rogue spectre like saren or the one from lotsb. Killing the boss with everyone still alive could offer lots of bonus points. The boss fight could only be triggered on some maps, and would limit the zone space for the duration of the boss fight.
7-There could be mercenary factions, like the ones from omega, from the citadel dlc...
8-Having the option between more than one announcer. If possible, a male one, a robotic one like a vi, and a female one. I must say i´m a little tired of listening to the same voice. If Mark Meer and Jen Halle could do this part, it would be great.
9-More thematic weekly challenges, like one involving using a team made only of asari, only of salarians, only of engineers, only of geth, only of vanguards...
10-Transplant the original me3 mp game along with the new game, and allowing people to utilize their EA/Bioware´s account retaining their profiles in the me3 game. So the me3 mp would not die, but transition to the next generation. I love this game, and I would play it for years.