1. Eventually the payout of the blocks go to zero, as we all know, and I think that's what Evan was saying?? At that point, we should have A: enough people using Dash thus more fees would be collected and B: a high enough value to make the small fee payouts worth a lot. It can never really go to zero, just almost zero. At some point though, fees will over shadow the rewards.
2. For interest rates, I suspect that Evan is talking about masternode services. You would pool your Dash with others, and reap a small % of the reward. These pooled accounts could represent a centralization issue if these big pooling companies garner a major % of masternodes and exercise their right to vote off of them. But anyway, this is basically already the service that, I belive, SpectroCoin wallet plans on implementing.