I think the day of a current player publicly coming out is a few years off yet.
Undoubtedly, who ever that player is, they will always get stick from opposing fans, as thats just how fans are. they will do almost anything to wind up the opposition.
It will take someone with a very strong will, though, as the barracking will unmerciful in some quarters, regardless if the clubs involved have a zero tolerance policy, or as it has and will become more excepted by widespread football society, and the numbsculls are shouted down.
I'm of the opinion though that it would be a lot easier if it's a player who is more widely respected by football fans of all clubs, than one who is just loved by his own club.
Fans will always have hate figures from other clubs, and players that they have more respect for. If someone like a Gerrard came out, as apposed to a Suarez, or a Lampard instead of a Terry, it would be a lot easier for a player of that calibre, than of a player who is a hate figure, or an undesirable anyway.
It's going to take a player with some balls to be the first to openly come out though (and no pun intended).