While there is of course no definitive truth to the rumor of him being Grayson, and the likelihood of him just being a soldier is there, I still really like the idea. Didn't Eastwood say his character was going to surprise people?
I've seen people say that the Agent 37/Spyral stuff is too recent to work into the movies...but we're also getting Cyborg on the League, Diana as the daughter of Zeus, ARGUS being present, etc. Coupled with the fact that Grayson is easily the best thing to happen to the character since the 80s Titans stuff, and I can see why it would be appealing to DC/WB to latch onto it.
And Tim Seeley (one half of the Grayson writing team) is taking over the Suicide Squad book next month, with some crossovers between the two titles in the works...
This is all speculation of course, but I don't think the idea is as out there as people are making it out to be.