I still believe it should be Valve's call on something like that, as a general case.
As a specific case, Valve already made that call when they took dustbowl's layout and copied it for goldrush. They effectively said "we think the layout can work for payload, but it needs significant changes, so we're going to create a new map rather than just modify dustbowl".
Trying to convert dustbowl to payload has always seemed obtuse and redundant to me.
