If Robin gets in as a FE newcomer I can't imagine them cutting Ike.
Marth stays cuz
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I believe Robin is more likely now. Because one of the first arguments to jump up was "Will they choose the male or female version?" which wasn't much of a thing against him/her anyway.
But I also see Robin more likely than a new lord because of what Robin brings to the table.
Ever since Sakurai stated he wanted to bring unique movesets to SSB4, and that he'd have less focus on the ammount of characters, I already suspected he wouldn't be adding characters just to fill the roster up (I even think he said these very same words).
So since Marth has the speedy/elegant swordsmanship, and Ike has the brutal/heavy swordsmanship... Any character added from F.E. that uses a sword will be redundant. That's where ROBIN comes in.
Robin would probably have a style of its own, be it magic/swordsmanship, be it controlling F.E. unit sprites, or a shifty weapon style, anyway they go around it will make Robin considerably different from the other F.E. characters. Not to mention that the Tactician/protagonist class would be represented in the vein that Pokemon Trainer represented the avatar who the playar controls throughout the whole adventure in Pokemon.