Trying to reduce the time it takes to reupload a save because you accidentally dwanded a tiny fraction of it.
Do it over TCP. In fact, let me show you what I was thinking of for a new upload system:
The first attempt to upload the save will be done by directly connecting to the server through TCP. That's normally easy because when people port forward, they often select both TCP and UDP out of ignorance. In addition to that, Blockland port forwards through uPnP with both TCP and UDP. RemoteControl takes advantage of those mechanisms by listening TCP on the server's port.
If this fails, then there are a choice of hosts that (1) the server will connect to and (2) the client will upload to:
My server
Any other person with a spare server (specifically you, Null)
My server at home
Any server can deny an upload (or be unresponsive) and the uploader's client will seek the next server in the queue.
If all pieces fail, the original upload-through-commands system will be used, which is what it is now.
Privacy is expected, avoiding uploading through other servers will be possible.