Took a quick look at both Assembly and Slotted.
- Their taking minimum 10% for the introductions. Looks like they could take more depending on their actual participation/funding. But I don't see them guaranteeing anything beyond introductions to other developers who join their site.
- I agree with Michael that you could be spending more time managing the project than you do developing it now if you really want it to take off.
- I like the idea of a simple online sign up platform. Mostly because I manage a FB group for a resort in Mexico and I have need for a special type of rental calendar where Fractional Owners can place their available weeks (individually and securely and without me babysitting the sheet) on a single sheet that visitors to my group can look at and automagically reserve time or contact the owner of the slot. But I don't think, at least as it is, Slotted would do that.
- Given the above, I would suggest you focus on features more attuned to small business or social signup and also make it mobile so that people can show up to the event/venue they signed up for with a confirmed reservation (for services, a table, a room, a contribution etc) on their mobile device. And social so that multiple participants can contribute to the signup sheet. There are, of course, many third party services that make and market these sorts of reservations services for small businesses. So if you could somehow take them out of the picture (to some degree) and at the same time remove some of the friction/cost in their reservation process, then I think you will have something easier to market and add features too.
It did not go over my head that you are potentially looking for feature contributors like the ones I mentioned above and dev is a part of bringing in Assembly. Just not sure you will get them from an open source contribution like Assembly. If marketing is the sole purpose for engaging Assembly, then I think you will have the same problem attracting marketing people as you have engaging customers without them.
Good luck and I hope this at least, gives you new things to think about.