there's no point in discussing a quota because it won't ever happen.
big 4 teams don't win titles off skill, they win by splashing out tonnes of money. but there aren't enough english players out there to gain an advantage by just spending extravagant amounts in England, so they have to look elsewhere so they can waste their money effectively.
i'm a bit undecided on quotas. on the one hand, foreign players in the premiership could be attributed to be a cause the national teams poor performance, as the national team can't possibly improve if no one invests in english talent.
on the other hand, last season the transfer market within england was horribly inflated. foreign investment gives some countries a chance to challenge the power of rich clubs with good scouting and talent development rather than big spending. By looking at less inflated markets, clubs can spot young foreign talent and invest in it, which gives them some chance of standing up to the big spenders.
its really not an issue though, the FA eat out of the Big 4's hands, they're profitable and that's all they care about so they'll never do it.