Hi @vliegey, nice to see you joining the discussion!
The idea of 15MMM is to have a first testmapping and use the opportunity to start bringing the people together who want to describe/map the alternatives they know. It needs not necessarily to be the people of the alternatives themselves, but if they are public (facebook page, etc.) they will anyway eventually get publicity. Those who are not public, who want to stay within circles of friends, should obviously not be mapped.
This is only one of the many steps we can make towards engaging the different people, collectives and spaces for the Degrowth conference - and an opportunity to get some feedback on the tools and taxonomy, so that we can improve the mapping system and build up something relevant and useful for the participants of the degrowth conference, as well as the communities around it.
The first step for this would then be to find a date and place (Cargonomia?) for the workshop. And decide on a tool to use. Taking into consideration what you already have and the comments from @toka above, I think the Semantic Mediawiki would be the most appropriate tool for you to use.