@ Oasis
Sakurai commented on Mach Rider about ten years ago (being considered as a retro character), along with the Urban Champion (that game is boring), Sukpaon (he could be fun), Bubbles from Clu-Clu Land (...why=???), and the Balloon Fighter. Ultimately, the Ice Climbers made it in the Melee roster over them.
Actually, Sakurai considered the following:
Balloon Fighter - rejected because Sakurai thinks he would be useless when his balloons popped (really, what could he do without balloons? And just what would he do with balloons?)
Bubbles - rejected because Sakurai thinks she can't fight (well, how could she fight if she cannot even stop moving at her own will?)
Excitebiker - rejected because how can Excitebiker jump on his bike unless Sakurai has to put down ramps everywhere on the stage (even if Sakurai decided to have him fight without the bike, what would he do? Excite Punch?)
Urban Champion - rejected because he doesn't have anything interesting to offer besides simple punches (it is true... his game was really boring, at least Little Mac's games were more fun)
He added Ice Climbers because he thought it would be interesting to play as two characters at the same time.
As for Sukapon, some fans asked Sakurai on the Melee questionnaires why Sukapon isn't in Melee... and Sakurai apparently told them not to expect Sukapon in the future.
Some fans asked for Mr. Saturn to be in Smash because according to their logic, if Jigglypuff can get in Smash, so can Mr. Saturn. Sakurai told them that their situations aren't the same because Mr. Saturn doesn't have limbs to fight with. So he put Mr. Saturn as an item in Melee instead.