Having an easy way to find a sub is a valuable idea. I’m not trying to rain on your parade, I’m putting out questions that I would think about before I did what you’re doing.
considerations I perceive:
1) Are you planning to monetize this? If so, how?
2) How is what you’re doing different or better than just having a local facebook group?
3) Personal security (in the wake of the group-ex instructor murdered over the summer) – who can see the website requests? I don’t necessarily want anyone other than my clients and 1-2 subs knowing about the location and time of my secluded classes.
4) How will you vet the qualifications of the instructors?
5) Employers may not want your subs – some places only allow employees to teach there.
6) Independent contractors may not want to provide their clients with access to subs they don’t know, whether for quality control or to control others’ access to their client list. At the places where I’m an independent contractor, it’s a lot harder for me to use a sub, because I provide specialty services and a big part of what people are paying for is me. I’m better off either cancelling class or working from a very select list of people that I know well.