submitting multiple proposals are explicitly allowed.
True, but be careful, for two reasons:
1) there may have been cases where people who submit applications to two orgs fall through the cracks, with each org thinking the other was going to take him.
2) passion generally drives success, and unless you're like my friend who didn't sleep and got a triple major in four years (and now heads chip development for a major game console), splitting your passion between multiple applications could reduce the chances of either one being accepted. Going a bit further with a single application, e.g. by including [more] working patches, seems the better choice... assuming you pick a project that the organization really likes, anyway.