OK, there has been some push-back about this.
If we drop it back to "recommended" we need to upgrade the interface so that:
1) Even though the user can still register with a hub (this doesn't use XML-RPC) the user is warned at registration time that they can not USE the hubs until XML-RPC is installed on the server.
2) It couldn't hurt to have a reminder of this at the end of registration as well.
3) The "Enable hub" setting in the hub module should FAIL to work if XML-RPC is not installed, and should tell the admin what to do.
4) The cron job that updates registration info on the hub should quietly be skipped when XML-RPC is not present.
I'll create some sub-tasks, Jerome.