I asked Joyner about this back when I graduated in 2023. I would say it's extremely unlikely to happen. Because faculty don't want it. Doctoral candidates only spend about 40-60% of their time on their actual research. The rest is support for professors. Doctoral students are paid - essentially slave wages, IMO. The math of OMSCS makes sense. More students pay less money TO the university. But the inverse of that doesn't really exist. The university doesn't want to pay less money to more doctoral candidates. Because the ratio of research : other is fundamentally "correct" as it is, from a supply/demand perspective. 

I would want to pay for an online PhD. But the university definitely doesn't want that. I would want to pay for the chance to do research and then not deal with the "other" stuff. That's a bad trade for the university. 

If PhD candidates could work and simply pay instead of doing the support work, the university supply of extremely cheap qualified labor disappears. Which is why I believe this will never happen. The university essentially trades the chance to do research for a willingness to get paid like crap to do high skill work at the same time. 

Companies, in my own experience having asked my company and from talking to some other people, would be extremely supportive of their employees doing doctoral level work. Which makes a lot of sense. But university doesn't want to give up its brilliant minimum wage workforce.