I don't think the proposal has been made concrete, but the way it has been presented to the media is that it would be to do with qualifying for the national team and therefore nationality based. Which would breach EU law. If FIFA wanted to they could introduce the UEFA rule and possibly expand it in terms of numbers, or limit non-EU players. Trying anything else (eg sport being given a special dispensation from EU employment laws) is highly unlikely to succeed becasue the EU are so protective of the freedom of movement of labour of its citizens. You also need to bear in mind that FIFA are likely to want the same rule worldwide which makes it even more annoying for them that one part of the world will effectively dictate the terms of the rule.