I’m pretty sure it wouldn’t pass permitting- I’ve had clients want to do the same thing and get turned down.

I made supper host status (my partners are rock stars) and starting December new ordinances require a permit to do air BnB and permits are not given to non owners. 

So you may need permits, plumbing, electrical, insulation, sheetrock and painting to get the place to the usual "empty house" status.

It seems I need ownership and insurance before I can get the permit.

Check with the city or county planning and zoning department to get an idea of what you can build and what is required for all approvals including site plan and building permits, proffers, water/sewer tap fees, bonding requirements, inspections and CO process and time frame for all approvals.You also need to check with the utility companies and get an idea of availability and cost estimates from them for water, sewer, power, gas, cable, installation and connection requirements, tap fees, hookup charges, transformer location and relocation, power line and power pole relocation issues.

As mentioned above the ADU play is very big right now as the city has done some big things as far as ADU allowance and ease when it comes to the permitting and planning piece of that but you are pretty spot on, this is why unless a crazy deal comes my way (off market will be the only way to make that happen) I am sticking to flipping locally and rolling those profits into buy and hold properties out of state.

In Wake county, development fees have exploded and, per a builder I talked to about two years ago, just getting permitted and utility taps can exceed $50K in Holly Springs. 

I already have the permit, but a company quoted me 20,000.

Is it still possible to create this ADU or is it not worth the effort to grab the permits?

We had somebody who decided to open a bed-and-breakfast nearby because it was a permitted zoning.