I’ve had a BookBrainz account for a while now and I think its achievements feature might be of interest to other projects. After brainstorming about it for how it might help CB, I think some sort of achievement system that connects all the projects would encourage people to try out everything and would make the MetaBrainz project as a whole feel more connected.
What I am thinking is that your MB profile (or maybe there could be something new, like a “MetaBrainz Passport” that lets you log into all the services and collects all your data across all projects in one place) would have a section that would collect achievements from all the projects. Like you could get some from listening to 100 unique artists on LB, or submitting 100 songs to AB, reviewing 100 albums for CB, adding 100 new works to MB, etc. Basically gamifying things in a way that encourages you to check things out that you might otherwise miss, and, in the process, contributes data for building the project as a whole.