Just checked the BIP, thanks for sharing.
Good motivation, actually, almost in the exact day and hour that this BIP is committed to github (few minutes sooner?), I started a topic
here regarding the same issues! I was surprised even more when I found both my article and this BIP share the same idea of separating coinbase transaction and the rest of the transactions committed to the Merkle tree. I take it as a very encouraging sign
Now bad news:
Unfortunately the BIP fails to achieve decentralisation improvement in a considerable fashion.
Imo, it is due to the fact that this BIP is a conservative, second layer tweak to Stratum to help miners building
the work by choosing the transactions they wish to confirm from sources other than the pool.
Sounds good but it is useless, I afraid.
Besides keeping the pool in charge of accounting, which is problematic anyway, by keeping its role as a hub that can accept or reject miner's submitted shares, it keeps the power to enforce its policy. Specially when it comes to signaling and governance issues, we would have the same situation with pools as always. Nothing is going to be changed by this BIP.
So, sorry my conclusion is: Good motivation, weak design because of the definite lack of courage to go deep down in the PoW itself instead of remaining in the shallow area of Stratum.