From a customer's point of view, the idea of having one site where I can find quality guiding worldwide appeals to me. In areas that are not renowned riding destinations it can be hard to find guides, especially outside their main season. So, essentially, I think it's a great idea.
Still, the initial investment is substantial, especially if you factor in the time you have to spend getting permits etc. Yes, you'd have to do this anyway, but still. So, for someone living in an area not known as a riding destination (or even as an outdoor destination) who just thinks about doing some guiding on the side and knows he/she will have to work a regular job, it could be too much. Also, it seems to be clearly aimed at one day or even 2 day rides. From what I've heard from various guides I've ridden with, half-day rides are quite popular (ride in the morning, spend time with your family/girlfriend/non-riding friends in the afternoon). Cheaper, and guides don't have to organize lunch.
Also, but this isn't specific to what you offer here, I sometimes wonder if it would be possible to have a "low key" guiding operation. Often when I'm in an area that's nor really remote, I'm looking for someone to show me trails, nothing more. He doesn't have to bring lunch/snacks, she doesn't have to repair my bike trailside (I can do most trailside repairs myself), and if they know how to stop a wound from bleeding, great, but my riding buddies aren't all so hot at first-aid, not to mention all the times I ride solo. So, just trails, no other responsibilities. Like a riding buddy showing you some new trails/a new area he's discovered. Probably legally impossible, but it would be fun. And no, it's not always possible to contact locals through the internet, and even Trailforks doesn't have everything.