I think a cool feature would be to add a toggle in the "edit budget settings" --> General Pool Rollover settings, that creates logic to roll unused budget from certain or all budgets into "savings goal/budget" type of object.

The use case would be if I wanted to save up for a specific thing and the strategy was to underspend in other budgets, this would be a mechanism to keep the funds in the bank account (not move it to a segregated account so it's "out of mind").

Then, budgets reset following month as normal, underspent rolls again into the "savings goal" object, and so on. Bonus points if for longer term/high dollar savings goal it calculated the estimated number of months remaining until the savings goal is hit based on average cash underspent and rolled in to the goal each month.