It's very unlikely that you'll see this type of proposal included within bitcoin, but there are alt-currencies planning the first few tentative steps towards your idea.

I believe darkcoin is the kind of hybrid situation where miners discover new blocks, and those with coin can run proof of stake nodes that are required to promote the anonymity in the network.  (darkcoin is essentially trustless coinjoin built straight into the client by default)

In the end, both types of supporters get paid the block rewards and transaction fees.