In another example of "why hasn't Capcom made this?", here's Mega Maker from WreckingPrograms. Mega Maker is a program designed to give you all the tools you need to create your own classic series inspired stages. You can even upload your stages and share them with other users!
Mega Maker is set to launch next Saturday, July15th. It's a free program – however, donations are being accepted to help run and maintain the server, which is necessary to share levels with your peers. You can help the servers here. Keep your eyes peeled to the official website for more information and updates!
Thanks for the tip, MegaBoy!