CASSANDRA-8523 it was added support to forwarding writes to a replacement node via a new gossip state BOOTSTRAPPING_REPLACE.
Currently this is limited to replacement nodes with a different address of the original node, because if a replacement node with the same address of a normal endpoint joins gossip with a non-dead state, it will become alive in the Failure Detector and reads will be forwarded to it before the node is ready to serve reads.
This ticket is to add support to forwarding writes to replacement nodes with the same IP address as the original node.
The initial idea is to allow marking a node as unavailable for reads on TokenMetadata, what will allow the replacement node with the same IP join gossip without having reads forwarded to it. This will be enabled by CASSANDRA-11559.