I don't really think Snake is first to go, but he is low priority. That's based off of my reasoning about his friendship with Kojima. I guess it just really depends on if Kojima wants him to stay and how Sakurai feels about that. I mean honestly, from the interview where he mentioned Snake and Sonic being a success, it really makes me think that if Sonic stays, that Snake will stay.
At this point, I think it's tough to determine who will be cut. I think it's fair to say that being a clone doesn't necessarily make you a target for being cut, but moreso for a moveset change (looking at you Falco and Ganondorf). So it's all a matter of what a character means to the game, and the series that they represent.
Wolf is important to Star Fox as a suitable playable villain. He has appeared several times, in basically every title (I think the only one he didn't was...Adventures?) He is already pretty different from Fox, so if Falco has a new moveset, all three are essentially unique.
Ike is important to Fire Emblem as a Lord that stands out based on his popularity, and his representation of Fire Emblem in the West. He has a very unique playstyle, and could be considered a representation of the console Fire Emblems, in which he appeared as a main character twice. Honestly, I don't think we'll see him leave. But if he does, and there is DLC, he'll be back.
Lucas is the main character of Mother 3, and plays very similarly to Ness. Honestly, I could absolutely see him getting cut. Don't ask me why, but I could definitely see it. However, I could also see him getting a different moveset. He will not be replaced by a different Mother character. It's either him and Ness, or just Ness.
Lucario is a very popular Pokemon who is important to Game Freak and The Pokemon Company. He has a unique moveset, and has remained important to Pokemon since his debut. He COULD leave, but leaving the roster with all Gen 1 characters isn't a very good representation of a series with 700+ Pokemon. I think he'll stay, and we'll gain Mewtwo.
Ice Climbers i'm positive will stay.
Pokemon Trainer, I personally think, may be low on the totem pole. If they have technical problems in trying to get him to work, then I could see him leave, and I don't know that I would honestly be all that upset. It's a cool character idea, but I honestly don't care if he gets cut.