SUGGESTION: Gonna knock this out in one suggestion,
a. being able to play as a lone wolf in offline mode or when the lobby is empty except for yourself would be nice. Or even better, in my opinion, be able to pick how many CPU ops you would like to play with.
b. as someone who likes to play with an offline character as well as an online character, for offline play, being able to customize your teams loadouts would be both helpful and aesthetically pleasing.