A small change to the protocol is proposed for satoshi client v0.7 (upcoming release):
Add 'mempool' P2P command, and extend 'getdata' behavior
https://github.com/bitcoin/bitcoin/pull/1641
The genesis of this command is to permit SPV clients to access the memory pool, but secondary uses include diagnostics and miner download (so that miners won't miss lucrative TX's due to node restart). "getdata" behavior is extended to include any memory pool transaction, relaxing a previous "getdata" restriction.
Didn't feel this warranted a BIP, but can write one if people really want one.