I think Nintendo franchises can be put into tiers that indicate the likelihood of inclusion and, to a slightly lesser extent, how many characters they will have.
I mean, Mario (and his related subseries and such), Zelda, Pokemon and to a lesser extent Kirby (who would probably be "second tier" in America but who more globally is a first tier- also, it's Sakurai's baby) are the biggest franchises in Nintendo. Even people who haven't played a game in those series are at least likely enough to know what they are, and in the case of some Mario and Pokemon characters, even people who haven't played ANY video games know who they are. Also note that all four of these series have had adaptations in TV and/or movies. Not surprisingly, these are the franchises best represented in Smash.
Metroid is sort of a "1.5 tier". Few would argue it is in the same level as Mario, Zelda and Pokemon, but it certainly it is above Fire Emblem (at least in America), Star Fox, etc.
Then there are franchises like Fire Emblem, F-Zero, Star Fox and Mother (again, it wouldn't be second tier in America, but it's popularity in Japan and critical acclaim gets it up more. Also note that the fact there has only been three Mother games is more because of Itoi's wishes than anything). These are series that, while critically acclaimed and popular, don't make as much an impact outside of the gaming culture.
Then there are the post-Pokemon Nintendo franchises that just haven't been able to get into the higher tiers (possibly because they have been overshadowed by the continuing dominance of Pikachu), but could as time goes on. For example, Pikmin could probably get up higher, but it only has had two games. Golden Sun probably will be able to one day get up, but only has had three games that, while well respected, haven't had as much impact as those franchises on the higher tiers. Ditto for Sin and Punishment, Animal Crossing (which would be higher... if there were any smashable characters), etc.
Then we have the other franchises, mostly from pre-Pokemon days.
Then there are "one game wonders".
And so on.
Note that third parties can go the same way: Sonic and Snake are iconic and both have made appearances on Nintendo consoles.
Note that I didn't place Kid Icarus anywhere, since we'll have to see how Uprising does before we can place it.
Feel free to comment.