This is a great organization. I've been a gsoc student 2 years ago and learned a lot from my project and earned a decent wage. Google pays hundreds of thousands of dollars for Open Source contributions done by these students.
It's worth noting that GSOC has become really expansive in the last couple of years, approving 988 projects last year alone. While that kind of expansiveness is great, I don't think it should be held as a prerequisite -- even if companies only did 10 or 20 sponsorships like this every summer it would have a really good impact.
Those sponsorships exist already -- they're called internships.
What would be great would be a FOSS-only list of internships and push for a change where a remote internship was more common, which I think is more what you're getting at with how GSOC differs from existing options.
The biggest difference is that GSOC does not support Google directly. Plenty of the projects Google supports this way are not even useful to them at all: for example, a silly 3D game I used to play was part of the program for three years. Internships are great, and there are some open source companies that have really neat ones (Mozilla comes to mind), but most small projects run by volunteers can't afford to pay for an intern themselves.