The few people I've know who have opened such businesses over the years have found the volume of customers to be insufficient plus those customers are too cheap to pay rates high enough to cover business expenses.(posted 8833 days ago)Those expenses include rent, utilities, various licenses and in this special case, lots of expensive hardware, insurance on that hardware, high liability insurance, and perhaps special equipment in order to comply with effluent regulations.
Also bear in mind that the photographic darkroom is a vanishing species; more and more things are vying for leisure time, more people want to play with digital etc.
Anyway...I think it's a great idea that's sorely needed in most areas but it's almost certainly to be a money-losing enterprise.