We tried this a few years back, and were only partly successful. Were still do the trips (self-supported MTB trips)for small groups, mostly as skills-teaching sessions, but on an occasional basis. Most of our clientele are missionary students, (primarily Lutheran) seeking training for travel in the Third World environment. We led a successful trip in Russia a few years back and built on that. Our primary emphasis, however, is first aid/medical training. About once every other year we put on a Wilderness First Aid Bike Trip and ride half a day, teach half a day. It is certainly a niche-type thing, but we found that tours alone wouldn't cut it here in MN. We have seen two other start-up bike tour services come and go in the past few years.
Personally, I think you are too late in the season if you plan to start this year. The big names like Cycle America and Western Spirit (not to mention ACA!) have been booking trips since February, which is when their brochures come out.
Hans Erdman, WEMT
Backcountry Trail Patrol-MN