A "Mike Myers" mode would be good seeing as there is a lot of people who play it. Basically, one person is assigned as "Mike" whilst say 11 others are on the other team. Mike has a knife and has to find everyone else and stab them. The other team have nothing apart from maybe flashbangs and can choose perks etc. (e.g commando pro). Then when there is 1 player left with Mike, both players are issued machine pistols and then they can duallll western-style biatchez!
Only thing I don't like about more modes is that it it spreads everyone out and makes the current ones thinner. maybe drop some of the less popular ones if you're bringing in more.
They should set it up like it was for CoD5, have a section for hardcore and regular and include every game mode they have to each section... They should add a "No Kill Cam Team Deathmatch" game mode!