Not sure if this idea has been brought up before but Im gonna suggest it anyways. Keep in mind Im assuming the pick 10 system is out the window and we're back to the original formula of primary, secondary, tact, lethal, equipment and perk 1,2,3.
I think the create a class system should be broken up into 3 tiers.
Tier 1 is your weaponry: Primary, Secondary, Tact, Lethal and Equipment
Tier 2 is your perks
Tier 3 is your killstreaks.
This way you have options to change only your gun if necessary or only your perks if necessary during mid game. Why I'd want to change killstreaks is if you're running high streaks and you're having a bad game then you can opt to change to a lower killstreak class. The condition to changing killstreaks mid game would be that any killstreaks acquired whilst using your current killstreak class must be used before you change, that way people cant just stack up streaks. --- http://www.youtube.com/watch?v=sw9O9RDQ_yA