Requiring high percentages of affordable units in an inclusionary zoning policy, or a 40B development is a recipe for making them uneconomical for developers (this is why there are limits on this in the MBTA law).

Edit: I think they've also considered certain types of protected land in the worksheet and GIS layers they put out to assist local governments to determine zoning that works:

https://www.mass.gov/info-details/compliance-model-components