Safety becomes a big issue for this kind of thing. It might make sense to start by leverage a platform like couchsurfing which has a personal review system.

Good point; I think it would initially involve some personal vetting as well as starting at a local level. This could be made part of the listing process where the only way to get verified as a member is to allow a designated photographer if you're hosting, and some kind of social proof (LinkedIn?) if you're looking for a space. I think this is a bigger concern in remote towns and the countryside, though. For a city like Amsterdam, safety might not be that big of an issue.

I think that was the idea behind http://www.workatjelly.com

Yeah I saw them, but it seems like it's just a directory to Facebook pages that needs to be updated by sending an email. I think there's a good business case to make a nice website and app that would afford people a coworking space-like luxury, but at rather ad-hoc and personal locations.

Have a look at https://www.codiwork.com