Well it can handle x number of bathrooms to be assigned to the lots based on people's bidding capacity.

Not about apportioning per lot 'per fairness'. Centralized planning for 'fairness' leads to perverse incentives.

Exactly. Once that bidding [for bedrooms, not bathrooms as that’s what drives sewer load] completes, the NIMBY’s have won. It’s a small inconvenience that they can’t add a legal bedroom in their attic, but at least the character of their neighborhood will be preserved.

For any established neighborhood, that will overwhelmingly have already happened.

It’s a hard problem, because it’s a people and money problem centered around the space they spend more time than anywhere else and more money than they’ve spent on any other thing.