This is no big deal. Though I have a rough idea of how I would approach it, if others want to run with it, I have no problem with it. The approach I would take would simply create the "site" on the spot and would all be local. A dedicated webpage for sublime themes is a fine way to go as well. By no means am I a "web" programmer (I do web stuff as a hobby), so if more experienced web guys would like to run with this instead, I have no problem and say more power to you .
If JSON is preferred for the site, I already have a plugin that can convert the color theme PLIST to JSON and back in Package Control. I guess the site could also work directly with the PLIST as well, but I imagine JSON would be easier. My point is, you could easily run with either format and it should be easy for users to get the format you need already without having to spend time on that part.
Anyways, if this project is full steam ahead, I will hold on my work. If this project dies down, I will resume my work when I have time. I don't mind lending a hand to help as I have time as well.