I'm fairly certain this can be done with a playertype, but I don't really know. But you can't have the crosshairs in third person mode, so the third person would be like on Strato's old Spitfire.
Maybe you could kind of switch the third person and first person views. So you'd have no crosshairs in first person, but you would in third.
I know I'm wording this very poorly, but I think it is possible. I guess that would also solve the problem of people wanting a mod to have no crosshairs.