I still say Chrom is much likelier than Roy at least. Despite being well known, Roy is still from a game that never saw the light in the West. His Melee appearance was a failed promotion for FE6, which originally was to be the first game to be released internationally (but that plan got scrapped cause of the game's difficulty, hence why FE7 is so much easier).
Keeping that in mind, Chrom and Lucina's support will probably sky rocket when Awakening gets released in the US and EU. And based on what the Japanese say, Awakening is probably the best Fire Emblem title since a long time. And it'll probably be well received over here as well, as the Japanese really love their Fire Emblem badly (with all rights).
Personally, I wouldn't even say Ike is as guranteed to return as people think he is. Sakurai could easily go lazy-mode and copypasta Ike's moveset on Chrom and call it a day. While I don't think or want it to happen, it could.
But anyway, Fire Emblem is a INTERNATIONAL series now, so why would Roy even be an option? And even crazier to me seems the idea Marth and Roy will look like their FE13 counterparts, but neither Chrom or Lucina are anywhere to be found. I really think either one of them, or maybe even both, will get playable. Even if they are to be 3DS-version exclusives.