Following a talk with @AlexeyAkhunov
Consider this model:
For every word stored in storage the caller must lock a fixed amount of ETH, say 0.001 ETH. When the storage being released, the caller gets this amount back, perhaps minus a small fee that get burned.
In this model, state size is limited by the total ETH supply. Moreover, as state grows it becomes more and more expensive to consume more storage. This is because consuming so much ETH to be locked in storage will become more and more expensive.
It is also easy to imagine transition from the current state to this model. There will be a grace period in which after storage that didn’t lock funds will be removed.
IMO it might be a simpler model of State Rent, supposedly still getting the goal of limiting the state size.