What makes sure that the custodians keep behaving well? It might pay off to get elected as a custodian, and then park all your nubits instead of selling them for $1. Or keep the dollars after selling a big amount. Did I miss something?
From the white paper:
"It is likely custodians will demonstrate they hold a substantial quantity of NuShares so that shareholders know custodians' interests align with their own. It is likely that at some point a custodian will disappoint shareholders, but the damage they can cause is limited to the value of the grant they have already received."
It's like in the real world: if you delegate power, try to be sure to grant it to the right person.
Parking needs voting from holders of NuShares as far as I got it.