I really don't think Ghirahim has a shot for SSB5 unless he's in another game in a few years. This is his era, there's a new Skyward Sword stage now and there won't be later, they'll have moved on to the more recent Zelda game - it's now or never. I think they kinda hurriedly put Ghirahim in as an assist trophy because they saw the popularity, and wanted to appease us, maybe he was more popular then they thought he would be. But after Hyrule Warriors, and if we keep asking for him, they might really reconsider how popular they thought he was and figure since they have the time and resources, put him in. Now maybe they'd be reluctant to scrap an assist trophy and would rather work on a character that hasn't been featured as much yet, but if there's enough petitions and stuff, he could make it.
However, I bet they gouged popularity while in development of SSB4, kinda like how they said the roster we have now was finalized...as soon as they started, based on popularity from Brawl and recent stuff (can't quite remember) but I remember realizing all our petitioning and pleading was kinda useless when they were already giving us reveal trailers. Buuut maybe it wasn't! In that time, they probably kept looking at popularity for DLC characters. Now I dunno if Ghirahim was close to the top or anything, but I figure they saw the popularity, put in an assist trophy, still see people asking for him, and figure they have time so...
Basically: I dunno! It's possible. But not for SSB5. Does anyone know how requested Ghirahim is in comparison to other potential fighters? I saw him on a lot of lists.