they probably mainly want feedback from the project maintainers at this stage, and the project maintainers can apply a patch just about as easily as they could apply a pull request. (It's so big that the web view isn't likely to be useful.) Also this will probably be going into a new branch if anywhere, so does a pull request to an existing branch (which is all that's possible AFAIK) even make sense?
Most projects have a process and gigantic monolithic patches that include entire new projects and "cleanup" updates to core all wrapped up in one are unmanaged and unmergable. It's for the sake of process.
Pull requests are great, but it's not like someone couldn't apply the patch and give them a hand - earlier in the thread someone did just that.
We use Team Foundation for a few other things related to project management (personally, I'm not a fan), but not for source control.