I think this idea certainly has interesting parts. We would at least need the following parts: * Neural nets or similar trained models, which we could prove do

I think this idea certainly has interesting parts. We would at least need the following parts: * Neural nets or similar trained models, which we could prove don't leak information on the data they are trained on. * A way to combine these models, without access to their training data, in a way that works as well as training a new model on the union of the data. * A way to exclude spammers. If the models vote on each message, perhaps we would be okay as long as fewer than 50% of the contributors are spammers.