If the sell side is low, then it means there is too much demand and not enough supply. We would need to vote to create more NuBits. If the buy side is low then it means there is not enough demand and the supply may need to be reduced.
In the case of low demand, we would first try raising parking interest rates. If that remains ineffective, then that means we need to permanently reduce the supply, and we can do that by printing new shares, selling them and using the proceeds to buy back and burn NuBits.
We have the first problem though and need to print NuBits. We would not have a reserve because the custodian we grant them to would sell the NuBits on the market and then distribute the proceeds in a number of different ways decided by shareholders (dividends, share buybacks, development, marketing, etc…)
If the custodian sold the NuBits and continued to hold the proceeds of the sale on-exchange (Bitcoin, etc…) for when people eventually trade their NuBits back in, then we would have a reserve, but that’s not the case here as far as I know. Nu is reserveless. We instead offer a reward for liquidity providers to place buy and sell walls, so we don’t have to maintain a reserve ourselves.