Regarding federated labeling, you might be interested in some recent prototypes built on Flower that use forms of self supervised learning. By combining SSL with federated learning we can start to leverage unlabeled data and this will be a big deal once it becomes common place. I'd suggest looking at these two research papers that build on Flower and include members of the Flower team as authors:
https://arxiv.org/abs/2207.01975
https://arxiv.org/abs/2204.02804