I would think so. Especially since, for example, California law is now allowing the IGT S plus. Many people who get these, get just one machine and don't even think of spare parts (I have 4 spare MPU's!) so they may want someone to just fix their board for, hopefully, a nominal cost. I've been able to repair many of mine but I have some electronics background and, of course, I'm here on nlg getting help from the pros like you, especially with that awful Bally EVO I had.
I'd think there would be a market for board repair especially if you dealt with most common game manufacturers. I think it would be very important to advertise here since everyone will go to the internet, and likely end up on NLG.