There is a recognised problem (in a number of threads) that NBT supply can easily grow to meet demand, but there is not a symmetric mechanism for burning of NBT when demand falls. The current mechanism of parking temporarily removes supply but only exacerbates the increase in supply later, which is widely seen as a potential flaw.
Is it possible that custodians can also be delegated the power to buy NBT and burn it if supply exceeds demand, a symmetry to their ability to sell newly created supply if demand exceeds supply? To do this they would need to keep the funds raised from sales in a reserve (for buying and burning as required) rather than distributing it quickly to shareholders. Instead shareholders could receive a regular small percentage of this reserve over time for supporting the NBT peg. When required, part of the reserve would be used to burn NBT.
As a custodian might build quite a large pool by holding this back, there would need to be ways to ensure the honesty of the custodians with these funds (e.g. multi-sig, re-allocation to other custodians etc) and ensure they are held in a way as to not be too volatile.
Admittedly I raised this idea in another thread, here New mechanism to reduce NBT supply: NBT Burning, but that thread has not seen a response in a couple of days, so thought I would summarise the idea more succinctly.