Possible optimisation to bitcoin propagation
My concern would be that in the case where the recipient doesn't have all the transactions, the extra request(s) to get them would end up taking more time than just sending them in the first place.  Miners are scattered all around the world but are likely to be able to pay for fast connections, so I would expect connections between them to have high latency and high bandwidth.  In such a case it's better to preemptively send a larger amount of data (fast because of high bandwidth) than to risk a request/reply round trip (slow because of high latency).

Also, miners pretty often include transactions that they originated, or were sent to them privately, or otherwise have not been broadcast on the peer-to-peer network.  Consider mining pool payouts, nonstandard transactions, low-fee transactions which the miner has agreed to "accelerate", etc.  So I think this extra request protocol would be needed more often than not.

This could be a reasonable optimization for full nodes who are not miners, and thus don't need to receive the block urgently.  They might save some bandwidth this way.  But on the other hand, since they don't need to receive the block urgently, we don't care so  much about them, and it's hard to justify a major p2p protocol change just for this.