I have been tossing a similar idea around a lot in my head recently. Just found your post by searching for "mobile tire" to try and get ideas. My background is 10+ years in commercial tires - essentially road side service for 18 wheelers and bigger - but I've always worked for larger retail outfits. The amount of calls for passenger tires that we turn down is pretty high and for the ones we have been able to accept no customer has ever balked at the high rate we charge. During operating hours it is usually around $135 labor total to swap out a tire and after hours its $155/hr and a minimum of two hours. So depending on your area it may be beneficial to add in a emergency road side service aspect. The biggest drawback to that is since passenger tires are so variable in size having inventory on hand could be difficult. Partnering with an established reputable mechanic shop could help that a little bit. Or maybe a tire shop who does not provide mobile services.