> Make an examination authority. "Here is the national linear algebra test. Anyone who wants to try it, sign up, and come to this hall on this date." Everyone who passes, whether they studied at home or went to fancy U, gets a paper that says they passed it. Do it as a 12 year old prodigy or a 75 year old grandma, you get a diploma.

> Now, maybe there is already an authority that does this, I don't know. But it isn't very well known or authoritative.

Western Governors University operates this way. You can get a full, recognized degree that way (in a limited set of topics).