I have already suggested this as a new feature. Cockos still have not seen the huge potential that they can have with Media Items. With the help of routing and persistence, a reusability can be lifted to a whole new level with only minor adjustments (such as key or chord changes). I already do that with subprojects used as media items. But media items would be much better because I am not limited in sound design (I can not play Project and Subprojecte at the same time).