This could probably be done fairly easily by bundling Stratum (it's
not just for pools!) and allowing SPV wallets to ask Bitcoind to start
it (if you don't use it, there's no need to waste the resources), and
then connect to it. The point of using Stratum is that it already is
being used by Electrum, and that it might be an easier way to support
SPV clients than creating a new API in bitcoind for it since Stratum
itself already relies on bitcoind to provide it's services.