I think this is more task for Microsoft to do...
It should not be GitHub, it should be a separate site. GitHub is for code, not shapes.
I think this is all about the App Store thing. I believe you can vote for it here, but I am not sure if it brings much:
https://feedbackportal.microsoft.com/feedback/idea/a084dd51-e01c-ec11-b6e7-0022481f88a4Anyway. Preview and search are essential, without them the whole site doesn't make much sense IMHO.
But previews and search require parsing Visio files (preferably on server).
To me, the only lib that is capable of doing that more-or-less "okay" is Aspose.
But it's commercial, and quite heavily commercial (they have a new
cloud API now though, and free tier there, like 150 calls per month).
Maybe they would agree to sponsor such a project, though.
Another question is copyright and shape licensing.
I am completely lost here - some shapes may be commercial or copyrighted (in fact, most of them are).
How would you suggest to deal with this?