While --no-ff is certainly useful it doesn't really do anything to clean up the stream of the (most likely, redundant) pull request. Pulley reduces it to a single commit instead (which I, and other contributors to jQuery, tend to prefer) and yet still closes the pull request automatically (which --squash doesn't handle).
(Some anecdotal experience: I believe that some members of the jQuery team tried to use --no-ff but it didn't seem to yield a result that reliably closed bugs on our bug tracker - not sure what the root cause was. Either way, it's not providing a formatted message, which is something that we want.)
I guess I'm confused about what you mean by "clean up the stream" and why you find it desirable. If someone fixes a bug by making five small changes, and documents each change with an intelligent commit message, I want those five commits in my history as-is. This also saves the contributor from having to rebase their repository.
I think you may be, severely, over estimating the quality of contributions that come in from random people to large projects hosted on Github. The pull request process tends to be highly iterative. Someone sends in the request, we send back suggestions, they make revisions - the back-and-forth continues until a final state is arrived upon. The nasty code that existed in the interim is really not of any use to anyone (and that's saying nothing of their general ability to write commit messages, which is generally lacking).
Anyone that demonstrates a repeated ability to make pull requests that require no revisions (and that have commit messages that are useful) are just given straight-up commit access (thus this particular tool does not apply to them).
Github link: https://github.com/jeresig/pulley