While not directly related to hair regeneration, I think this could be another way of getting there (a potential cure). ReCell was just approved by the FDA for healing burns. It’s a fantastic technology and requires 97% less skin than what was used with older techniques to cover burn wounds. So if your whole back was burned you only need a credit card sized area to heal it.
The main reason I’m posting the articles is for the images (but they’re an interesting read too), just look at how amazing the results are (warning not for the squeamish). Now their articles don’t seem to explicitly claim it regenerates new skin but that’s what appears to be happening (see photos).
Bottom line is that if it can regrow the top layers of skin along with hair follicles then imo this could be one possible cure for us that is basically available right now. The way I see it working is that a doctor would take a small biopsy of skin cells from an area of your head where hair permanently grows, then remove a thin layer of skin from the bald areas and spray on the skin cells and when it heals you should get hair growing also.
If that doesn’t work, you could do a strip hair transplant, spray on the skin and you should get your old hair growing back-repeat until you have a full head of hair. We just need some hair transplant surgeons to try this idea out. Of course, it rests on the premise that the skin regenerates and doesn’t scar, so hair can grow on the healed area, hopefully, it can.