Postby Chad » Wed Jun 25, 2014 2:32 am
The only limitations Peach and Toad really have are the inability to ride Yoshis or slide, and in Peach's case, no spin-jumping. Even the latter can be solved by designing areas so that where spin-jumping is necessary, Peach can still hover over those parts. As for Yoshis and sliding, hardly anyone makes use of those. Boots aren't a bad substitute for Yoshis, but filters can be set up if they're really needed.
So there are a few limitations, but if you can work around them (even if it isn't in a graceful fashion), you should be good. It's best that you do if they're playable options, but if you'd rather not go through the trouble, don't make them playable.