Politically Correct stunt, nothing to see here. That said I imagine the whole "coming out" issue will sell a lot of books, and that's the big point. If it tanks the title they can always retcon it later.
I say this is a PC stunt because out of the iconic characters pretty much every one of them has a love interest, many have been married, and we've even had kids running around at various times, sometimes from alternate timelines, sometimes not.
Aquaman has had his queens and mer-babes, Superman has had Lois Lane, Batman had his big things with Catwoman and Talia and has a son, etc... even Martian Manhunter has had his past loves.
At this point pretty much all of the iconic characters would have to be retconned into being gay. Except maybe Wonder Woman (if they said Lesbian) but her being bi- kind of falls under the "duh" catagory, though I imagine they could spend some time on who she's been with to be shocking (ie other iconic or well known characters at times, behind the scenes). I suppose they COULD work with second stringer heroes using an iconic mantle, like say some of the "also ran" Green Lanterns that also have the name.
I'll also say this is lulzworthy because DC actually runs an entire imprint called "Wildstorm" that is full of LGBT characters. Noir, Apollo, The Midnighter, Sarah Rainmaker, Swift (Bi), etc...
Heralding this entire thing has been this whole supposition that DC needs to catch up with other comics companies in the arena of political correctness, but really it's probably been at this longer than say Marvel as it has LGBT characters who are still in print to the best of my knowlege. This having been handled better than say the whole reveal that Northstar was gay in Marvel from years ago.
There isn't really any stopping them, and I suppose in the short term it's a good move because of the sales it will generate of whatever title they pick. In the long term it's a ret conning nightmare that is probably going to play havoc with continuity, especially given how much the whole "I must save my girlfriend" thing has been used as a motivating force for any of those characters.
To me the funniest character for them to say would be gay is actually Hawkman (as opposed to Aquaman) I mean girly wings, leather straps... he fits the image. Of course it would be lulzworthy because Hawkman is the character who is probably most based around his heterosexuality as a big part of his storylines has revolved around his girlfriend and how if he and his soul mate ever get together death/doom follows. I suppose technically they could have his soul mate reincarnate as a guy, but that would kind of be pushing it in saying "he was always gay". This aspect of the character was brought out and used to beat you over the head in part of the whole "Darkest Night" / "Brightest Day" thing a few years ago where he had a whole scene about that with Hawkwoman.
That said in other things I read on the subject they didn't say "gay" flat out, but seemed to dance around it. That lead me to believe that they were finally just going to spell out the nature of Wonder Woman's romance life, which would be the one iconic character they could say was always that way, without much in the way of retconning.
Also, isn't Plastic Man gay already?