It’s a good point that the proposed rule affects the number of players allowed on the pitch, and not in the squads; but I still think you’re mistaken: it *is* an employment restriction. An EU player is paid in order to provide a service to the club: that (s)he must be able (but not guaranteed) to play competitive matches (and to undertake necessary training, maintain fitness levels…whatever). That is a contract that binds employer and employee: the player expects to be eligible to play matches except where (s)he cannot be reasonably expected to do so based on form, fitness, tactics, etc. One of those exceptions cannot, however, be nationality (simply because the EC treaty says so). Regardless of the how small the rule affects his/her chances of ultimately playing a game, if it does so in any way at all, it will violate EU law: that particular article about freedom of movement is deliberately non-specific in how it defines “employment”.

I agree with Ian in that steps to restrict general social or cultural evolutions rarely, if ever, succeed: I just don’t see FIFA having a case here.