the thing is, Ike is very different from any other Fire emblem character in Smash. In brawl he is slow and powerfull with it's own move set, he is added gameplay. Roy was merely a clone with tweaked stats numbers, which was also supposed to be a slow but powerfull version of Marth.
For smash4, in order to cut Ike they would have to make the new fire emblem character play like Ike (that's "kinda" what they wanted to do with Lucario vs Mewtwo but not very well because mewtwo is also unique). But the only obvious newcomer for FireEmblem as a Ike-clone would be Chrom and I don't see him as a slow type, he uses the same sword as Marth, not a gigantic sword like Ike with Ragnell.
Sakurai (and Nintendo in general for that matter) always see gameplay first and that how he decides which character to include above all. They'll likely won't cut such a unique character if they can't replace him with someone similar that fit the same role. (Snake may be an exception for legal matters, and ROB if they fells like the characters wasn't used enough (not fun to play ?) )
Also in the Fire Emblem serie, Ike may be the next most talked about character after Marth, He is feature as the main character in 2 games, he is seen as the most powerfull opponent in the DLCs, and even have an heir as a playable character in FE Awakening: Priam, which carry his sword (Priam could fit as a replacement for Ike but that wouldn't make much sense as he is no more than an easter egg at this point ).
So I don't think Ike will be cut, there is no one to takes its place as a slow and powerfull sword user, my guess is we will see a third Fire Emblem character, Chrom would be obvious choice but maybe to much like Marth as a fighter, except if they find a way to make him play really different (maybe with mobility).
Robin (myAvatar/ the tactician) would be the second choice, a very interesting one, combining melee Sword play and range magic. Also with the 2 genders option (like Wii Fit Trainer).
My personnal wish is that both are newcomers because I love FE Awakening but even then I don't want Ike to be cut because he is extremely fun to play and unique and no FE:A character can replace him.