A lot of people have suggested new game modes as well as new maps, which for any game like this is good and necessary. However, while things like Capture the Flag or King of the Hill etc. are fine, I think we need at least one game mode that's more engaging and isn't just another TDM variation. I also think new game modes are going to keep things more fresh than just having the same game modes on different maps.
So, a rough thought. Overall objective, minor objectives etc., all could be replaced by whatever fits most with the universe lore.
Sieging a mech assembly facility to either destroy it or maybe capture/heist "blueprints" for a cliché Top Secret mech. One team would be "Attacking", the other "Defending".
For Attackers, they'd have staged objectives to complete. For this scenario let's say there are turrets defending the big, main doors to the facility. Attackers can either assault a munitions building to stop the supply of ammo to the turrets, essentially disabling them, maybe they have to set up explosives at this facility ("plant a bomb") and then Defenders would have to prevent that by eliminating enemy mechs at that building and defuse the bomb if planted. Or, there could be a shield generator building as a secondary option that they can "hack" to disable shields on the turrets to let them destroy the turrets directly instead. Having two objectives, slightly different, could also allow the Attacking team to "split" push objectives and maybe try and sneak one while the Defenders are distracted by the other.