So it appears the Ethereum guys finally got around to the basic idea of a 5% inactivity fee we plan for BTS. They just posted an entire blog post about a new treap (tree+heap) data-structure for storing accounts. Apparently they expect people to use the same private key over and over again (with no consideration for privacy implications).
Anyway here is the thing to take away from their post.
1) The only reason you need a Treap is to support light clients. Light clients are great, but ultimately 'trust-free' light clients are impossible with a proof-of-stake coin.
2) This is a large amount of extra complexity is quite easily solved with 'proof of fraud' transactions and a surety bond. A light client would pay a small fee to have their transactions verified and if the verified party lies, then the 'signed lie' is sufficient to forfeit the surety bond.
Given DPOS and #2 we can simply forgo having to worry about light clients in the blockchain design at all. This allows us to use very simple database structures compared to what Ethereum is planning.