How many full nodes there are currently? What is the incentive to run one? What if they are DDoS'ed?
Is the bolded part a problem for privacy?
Are we talking about Monero, or in JustusRanvier's proposal?
Bloom filters are specifically designed not to sufficiently compromise privacy. They're used for SPV in Bitcoin, where you tell a full node a range of addresses you're "interested in", and it tells you about any transactions that come in to those. You're going to get a bunch of false positives, but not enough to care about. You can also still maintain a degree of consensus by connecting to multiple nodes and fetching block headers from them, verifying the PoW across the header, and then submitting the bloom filter to a set of seemingly honest nodes you find.
Perhaps he thought it's better to make sybil attacks harder. It's basically free to launch as many full nodes as required.
You can't Sybil attack JustusRanvier's model, because the micropayment happens per-action and between peers. Running a series of sock-puppet nodes doesn't help you, because your sock-puppets have to provide the same services as a full node to get paid. May as well just run a bunch of full nodes in VMs then (which would massively assist the network if every node was mixing and getting paid for it via micropayment channels).