Udpate on this regarding replication: After some more tests and investigation we identified the membership and gossip protocol as the main problem areas that make replication unreliable. Specifically, there is the issue with members not joining probably that I talked about on the mailing list and the issue with gossip messages looping in the network.
While trying to contribute a proper fix for this to Radicle Link we also want to work around this so that we have stable replication with seed nodes. The idea here is to restrict the connections of a peer so that it only connects with the seed node while the seed node is able to handle a lot of simultaneously connected peers.
If this is successful we should be in a situation where we can make the Upstream seed the default seed for Upstream, host our own projects there and have external people checkout and contribute back to our project.