Okay, I suspect I have more understanding of these issues than most on here.
At the present time, Article 50 has not even been enacted, so we're a minimum of 27 months from knowing whether a deal can even be reached on exit. There is legal provision for the two year negotiating period to be extended by mutual agreement, and it is far from impossible that both sides may decide that it wouldn't hurt to move the date past that of the next UK general election. In any event, given that exit would not be a done deal overnight, we're looking four years away in any realistic terms.
At which point, there will be approximately 6'500'000 people in the mainland UK on the basis of EEA nationality or ties. If you think that any deal is seriously going to look to limit the rights of those people - or of the two million or so Brits on the continent - then you are either a) insane or b) of the mistaken belief that the level of paperwork involved is even possible.
You may see a new limitation on Kolpak players in circa 5 years time. But if you do, any existing ones will be protected - those that have not met the requirements for citizenship that is - and arrangements will be put in place to support the freedom of top class sportsmen to move across borders. Yadda yadda exigent circumstances, national interest etc.