I was reading through the block compression techniques used in Graphene and suggested in Marlin as well. Perhaps the following method used in Kusama could be worth a look as well. It reduces address sizes to 3 bytes.
Most block compression techniques deal with transactions directly as a whole, Graphene tries to do set reconciliation of transactions and Compact Blocks replaces the transactions with ids derived from them. Compressing addresses wouldn’t really make a difference here.
Where I can see this helping is in the transaction propagation stage. A minimal Ethereum transaction transferring ethers is ~100-150 bytes, if the “to” address can be compressed, it would make it ~20-30% smaller. The returns are much lower in transactions involving contracts though.
My bad. Thanks for the detailed response. Will be on the look out and share anything else I find relevant.