I think the idea itself is interesting, but I think there'd be a lot of problems with it, since modified versions of PB wouldn't be compatible with the original, such you wouldn't be able to share your things in "Explore", though if you allowed people to make their own executables as well...
I think it'd create a huge discrepancy with the games different versions. I think it'd be good for testing out things, creating presentations of features you'd like to see in the main build of the game?