1. As with any social network system, the most difficult part is that you need a critical mass of users before the system becomes worthwhile, but to be able to get users, you already have to have traction in the first place, so it's a bit of a chicken/egg issue.
2. You say you're building a directory that features experienced devs. The next question is naturally - how are you going to verify these devs? Everyone is going to have their own definition of what it means to be an "experienced dev".
The fact that everyone just "lists themselves" means that by definition there's really no trust or verification in the process itself from a potential employer perspective.
3. It sounds like your goal is to basically be the white pages of experienced devs which is laudable enough, however, I'm still not sure I understand the buy value from an employer perspective. Why would they take the time to visit this random website as opposed to just running searches on people's LinkedIn resumes filtered by years of experience?