You already have external PhD programs at many universities, just their success rate is usually abysmal, which I believe is often due to non-MOOC basic classes

You already have external PhD programs at many universities, just their success rate is usually abysmal, which I believe is often due to non-MOOC basic classes they require. As you mentioned, those are often overlapping with advanced grad courses, so at least that barrier could be gone by time OP's kid is adult.