"Lets say you are about to deploy 100 relays within the next week." - Take
this an order of magnitude greater and we're on the right track with the
correct scale. It is a regular occurrence for our users to deploy 500 to
5000 nodes at a time. This is not the scale that everyone uses, obviously,
but in that case generating 1000 relay keys and coordinating that key
distribution dance across the same number of nodes (more than likely in
highly distributed environments) seems to bring more questions than it
answers (securing the keys for those nodes, securely distributing them,
etc). When compounding you concern about the network cost for "spare"
nodes, I would say this turns it into a no-go as the whole point was to be
able to deploy these nodes in the most productive, network friendly
mechanism possible.