Since I'm a Knight of Elibe now, I thought I'd throw in my two cents about Roy's chances, and how they ARE existant.
Now, we all know that Roy's FE popularity is pathetic to many of the other FE lords, that's a given. But his smash popularity is another story. He's become a pretty freaking popular character in smash (sword characters tend to do that) so he may simply return just for that. He's quite popular to competitive players, and incredibly popular to the casual players. I think he may have had the third (IIRC) strongest fanbase behind Marth and Link. Being the first GBA lord doesn't hurt his chances either.
Even if he is over-looked, I see a good chance of Eliwood's appearance in exchange. Roy was a very popular character in smash, and he's also a familiar character among smash players. Eliwood would be a familiar appearance to smash players thanks to Roy, and he'd be familiar to US FE players thanks to being in the first internationaly released FE.