1) The Boy (from A Boy and his Blob on NES and Wii)
The original "A Boy and his Blob" game is considered a great classic and its main character duo would had made for a very versatile fighter in Smash Bros. This is because the boy can use his blob for pretty much anything, making him a more interesting character than Rosalina who has her Luma as her sidekick. Think about it for a second, using the blob to attack, guard and do special moves by morphing it into various objects is something that would had made this character to be very fun to use. Many things come to mind when we think of potential moves. For example if you were to be falling down, you turn the blob into a ladder and climb back to safety or if you needed a quick weapon then you could turn the blob into a sword, shield or projectile. Possibilities are endless with this one.
Speed: Med - Defense: Low - Power: High
Final Smash: Turning the blob into a giant bowling ball, rolling it in the direction he is facing and decimating anything it touches.
2) Billy Lee (Double Dragon)
We already have a hand to hand specialist in the form of Little Mac, but it wouldn't had hurt to have the most famous of the Lee brothers joining the fight. This one would had been similar to Little Mac, but a lot more controllable as Little Mac tends to fall out of the stage a lot if you get carried away with the special moves. Billy Lee would not only be able to use his martial art moves, but also have special moves that include the use of various weapons that appear on the original game like the nunchaku, whip or bat. Billy trademark grapple would had to make an appearance too as many players loved using it in the original game. It would also be very cool if Billy had his whirlwind kick as a risky move to clear the area (sort of like Kirby's block attack).
Speed: Low - Defense: Med - Power: Med
Final Smash: Two big Abobo enemies appear on stage, following enemies and punching them into oblivion.
3) Ryu Hayabusa (from the classic NES games)
One of the coolest things about the classic Ninja Gaiden games were the anime cutscenes they featured which was something that wasn't common in games at the time. In Smash Bros, we could have the anime styled Ryu Hayabusa that appeared on those cutscenes using the whole assortment of powers and weapons that he had in the classic games, but with a little less speed than Greninja. Other than the moves and weapons, one cool feature that Ryu could have is to be able to climb the wall if he's falling and somehow can get to it in time, the downside been that you could be knocked down if hit while climbing and haven't gotten to the ledge yet.
Speed: Med - Defense: Low - Power: High
Final Smash: The Jaquio appears and starts throwing big lighting spheres across the stage, severely damaging your enemies.
4) Bill Rizer (Contra)
By seen Bill Rizer in the list you may be thinking that it would be kind of unfair to have a character that has a machine gun all time, but it is not. Bill would be a slower but more powerful version of Snake (Super Smash Brothers Brawl), only using his equipment at some occasions and with a limited range. He would also be able to change his weapon into some of the special ones he finds in the original games and use small grenades like Snake does. He would also be able to double jump and prone (shoot while lying on the ground) to compensate for his lack of speed. His gun attacks will also had to be be very strong to keep up in the fight against faster opponents.
Speed: Low - Defense: Med - Power: High
Final Smash: Bill makes a call and in a second, a flurry of big missiles (like the ones on stage 4 in Contra III: The Alien Wars) blowing away any opponent they touch.
5) Simon Belmont (Castlevania)
Almost everybody agrees that Simon Belmont should be in Smash Bros and it is not a hard thing to justify considering that the franchise made its console debut with the NES and also that Super Castlevania IV is considered by many to be the best of the classic series. Simon would be a very interesting character to play with, as the whip gives him a good mid range attack and his assortment of sub-weapons can make for pretty good strategies to use against opponents. He would have limited jumping skills but would be able to cling and make an extra jump by whipping the edge of a wall or platform at the right time.
Speed: Med - Defense: Low - Power: Med
Final Smash: The Belmont's super attack of choice, the Grand Cross.
Wrapping it up:
It was once stated by Nintendo that Super Smash Bros would never become a fan service fest, but considering how the franchise roster has been evolving since Brawl we can see that the purist notion that they had is slowly vanishing and that we may see a lot of interesting character appearances in the future. Let's just hope that they keep up the good work of bringing some of our childhood video game heroes back to life. Who knows? Maybe the Wii U version has some nice surprises in store for us.