I've looked through the existing issues and haven't found any related specifically to implementing this feature.

Advanced shard awareness is a feature that speeds up connection creation. It uses Scylla's shard-aware port on which Scylla chooses target shard based on the connection's source port. AFAIK it was never implemented in 4.x version of the driver.
3.x makes use of it by explicitly setting local port on boostrap.connect(...):

Evidence for it not working right now:
Started 16 shard Scylla node and run 6 session initializations simultaneously. With 9042 port multiple reconnection attempts can be observed in debug logs before initializing full 16 channel pool. This is expected and was checked for reference.

With 19042 port it seems that driver gets stuck on 8/16 channels. This is a weird result, but if advanced shard awareness was in use it should not be happening either way. I was expecting a number of reconnections of the similar order as number of random d16 dice rolls until rolling every number.

Expected result with advanced shard awareness enabled would be driver initializing all channels without considerable number of reconnections for all sessions, ideally none.