I think a GPL-like extension of a pencil sharpener would be the following. You develop a new pencil sharpener that copies 90% of the original design but includes a sharper blade that makes nicer pencil tips; when you release that product, you must show everyone how your pencil sharpener is designed and definitely must not prevent anyone from seeing how the original (that you started with) was designed.
I think both GPL and MIT have their place in the open source world. If you want to build something long-term and you want everyone to contribute, then use GPL. If you just care about jumpstarting a solution to a problem, and if you're satisfied if they only use your basic solution at the very least, then use MIT.