I think a fair way to see how Sakurai-san comes up with new characters is he literally breezes over everything Nintendo has released and asks if a certain character has any potential for something fun, and then asks if it is worthwhile. Worthwhile as in, will it be worth the time it takes to plan, design, draw, code, balance a character, and if it is worth the fun experiences they will bring. Of course staple characters like Link or Mario happen because they need to happen, and I am sure internally there are certain suggestions such as Ike, but beyond that, this would be a fair way of assuming how he functions. If you don't think that is a fair assumption, then correct me. It would fall nicely with what he has stated before, and
more recently.
It would make a whole lot of sense for characters such as the Ice Climbers, Mr. Game & Watch and Wii Fit Trainer. They are not really popular characters, and only Game & Watch could be considered vaguely pivotal, but if you were to sample their respective games, only Ice Climber would take much imagination to make into a fighter. Even someone like Captain Falcon is actually surprisingly simple in delivery: combining the high speed of his games with elements of super sentai, to reflect his name and image. While people are often upset because the series does not have such and such popular character or enough female fighters, i am sure it is more about the fact nothing really jumped out enough to design it, more so than the director having any sort of vendetta.
So going forward with this, I think trying to make the pairing system work in Smash Bros is a very natural evolution, since the characters and the way they interact with each other on the battlefield jumps out about Awakening more than anything. It could make for such a cool fighting style that is different from everything else. That said, it would require a massive workload far exceeding most of if not all the cast, and that's not even getting into technical issues. I am sure he would love to work in a new Fire Emblem character to fulfill fanservice,and would get advice from the creators to do so. I think IS, as well as the Pokemon Company, actually have a fair amount of say in what characters appear. Even if the three lords from Awakening don't seem interesting to Sakurai-san, I am sure that with how largely inconsequential the choice of Fire Emblem character is in terms of how they fight, he would make them work as he did with Ike.
When I see someone like Tiki or Anna happening, it is specifically because he has some crazy idea that we would normally not expect, but I doubt it. Ultimately, at the end of the day, I hate when people make up stupid rules for which characters can or cannot showup. Be it they are just a supporting character, not a fighter to begin with or whatever. All of this has been tossed aside before, and will continue to be discarded in necessitation of what is the most fun. if you were to ask me who I think is the most likely Fire Emblem newcomer, I would say "Chrom", though I acknowledge that they could have an idea for something that could make for a more fun game overall.
While I can't count on them to see the vision I have of Anna, I know Robin is a concept much simpler to understand, so I think she is a more reasonable expectation.
Sorry. 
