I guess there is also the 'issue' of what a drivers salary covers? i.e. is it just driving the car or does it include promoting the manufacturer or the sponsor brands. Drivers could easily circumvent the salary cap by being paid by a 3rd party company to promote stuff (including team sponsorship). That way it's not their salary! So I doubt it's enforceable either. I'm not even sure the budget cap is enforceable. Way too many teams working together will be sharing costs - probably not equally sharing costs either!