Bingo!
I like to look at medicine like most things in life using the 80/20 rule - meaning that 80% of cases are routine. That's true for pretty much for all medical fields. It's that 20% that you really need a physician with all the training that is involved. So, if you're an NP who wants to work autonomously, your job is to separate the routine from the complex cases.
This is where primary care and derm get into trouble with NP's. Like primary care, most derm cases are non-emergent. So even if you misdiagnose something initially, you can follow the patient on short-term follow-up - say within one or two weeks. After one or two follow-up visits and your treatment plan isn't working, what do you do? Simple. Refer the patient to a real physician, in this case a dermatologist. Again like primary case, what does an NP do if she suspects if the patient appears in serious imminent trouble? Send the patient to the ED, where a dermatologist can be consulted.
The reason why a field like surgery is less at risk from NP's is because the NP does not have the luxury of time or margin for error. If the NP accidentally snips a vessel, the patient is dead within minutes. If the NP cuts a nerve, the patient is paralyzed permanently. Then it gets into the media and the politicians will crack down on it.
But I suspect that most NP's want to do derm for the same reason why most med students want to do it. It's not for medical derm. It's for cosmetics. Like I said before, cosmetics is unregulated and practically anyone with the appropriate healthcare license and enough money can go into it.
If they can open up a medical spa now, why do NP's want to start derm residencies? I suspect that it's to be able to introduce themselves as "doctor" and to legitimatize themselves by claiming that they are "a derm specialist" because they are "board-certified" by some stupid nursing organization which will no doubt be created to accredit these residencies.
As someone pointed out before, these derm residencies are not under the control of the GME but under the nursing programs. They will spring up like weeds nationwide because nursing in general wants to push itself onto as much of medical turf as possible and because it will be a big money maker for the nursing programs because they will charge these wannabe nursing derms a lot of tuition money. If students are naive enough to hand over $50k per year in tuition for law or pharmacy schools where the job prospects are horrendous, then I bet that these derm residencies will have no trouble getting applicants.
So, bottom line, the factors that drove up interest in derm from medical students will be the same ones that will turn people off from it in the future.