We tried to do something along these lines in Melbourne, Australia. It was called Dragonfly. A few points:
- We emailed people to update their availability. If they were available this week, we'd email. Otherwise they could set their busyness to between 1 week and 3 months.
- We tracked where people were working and used that to bill the companies that hired them. First we charged a flat subscription rate of $3600 per year but people didn't want to pay that. We then charged $100 per week per freelancer. They wanted to go back to paying the subscription again. Then we went broke.
- People won't keep their availabilities up to date. They won't like you asking them to keep their availabilities up to date either. They really won't like you asking them where they're working this week.
- People will ask you how you're curating the list. If you're not curating it, theirs no point in using it as I can get list of people to hire anywhere. I want a list of people that are good at what they do.
- Recruiters function because they hide the cost of hiring freelancers. You're a design agency, your charge out rate is $250/h. Hiring this gun front end developer through a recruiter costs me $100/h. I make $150/h, simple math.
The most important things to solve from POV is how you're going to curate the list and keep the bad coders off it. You want to start with A's and only have A's. As soon as B's creep onto the list then your reputation goes down. Also, because you want to keep showing growth, C's and D's begin to creep onto it. Also, your friend who you like but sucks at JavaScript will ring you up and ask to be placed on it.
Good luck.