Role system would advance MP gameplay, this would allow players to take distinguished roles and keep the track of what everyone is doing. If you notice a lack of air superiority fighters, you can take this role and let everyone know your intentions. Same for SEAD/DEAD/CAP/CAS/Supply and other types.
Currenly we don't see what roles players took, we can only ask them or look at 3rd party GCI tool if transponder is set, and not everyone uses chat/voice chat. On big servers it's a problem. When I fly, I need to know how many people are engaged in SEAD or ground attacks, so I could judge if we need another CAP fighter.
I have a good example of it:
This would provide environment for basic teamwork. From here, we can judge who does the role best or which role don't have enough firepower and people. This won't limit players, since pretty much every aircraft is partly multi-role, but for proper job they need to know what exactly is needed on a battlefield.
This is especially important for upcoming RTS engine, since we need to know how many people throw to supply lines and how many people we need to counter advanced enemy SAM sites.
This could also help to popularize CA since this would become a set of dedicated slots. A squad of people could perform tasks on a ground based on muiltiplayer mission.
Additionally, assigning players to independent squads not only in voice chat, but also in the game itself could eccourage people to cooperate and bring players together to complete a common task.