NPC wings are already in the game, we just can't join the wing. There are also SLFs that act similar to a wingmate.
Basic crew / SLF fighter commands are already in the game.
Wing functionality is already in the game.
There is even a tutorial in the game where you are part of an NPC wing.
Persistance issues can and have been overcome before, or to start they could limit wings to being only available on certain missions.
So which part of this is the issue.
No issues from a technical feasibility perspective, but there is a laundry list of features to develop. I can think of the following off the top of my head:
UI functionality to hire and fire
Coding to tie NPCs into the mission system
Mission difficulty changes dependant on whether you have wingmen or not
Additional voice comms
Additional AI functions for NPC behaviour dependant on what you commend them to do - there were dozens of options available in Falcon4
Engage and disengage AI functionality - you wouldn't want the usual forum reaction when your wing-men don't disengage and end up fried would you?
Entity ownership during multiplayer engagements and transferal if needed if there is a single owner in an island that isn't the controlling player
Persistence between star systems, supercruise and islands
Beacon functionality to do with the above
Many other bits I haven't thought of...
Issues would therefore be time and resources being finite and code and assets not magically springing into existence, no matter how hard we wish it to be, or whether someone has done it before. Sandro has given a response that they see issues with game balance and that is also a consideration before you even commit to the the items above. This is why "the other game" is in the state it is in. I think there is a film quote that goes along the lines of "just because we can do something, doesn't mean that we necessarily should"...