We need some kinda shortcut: like, run your app for a few days on an instance, we chew your stackdriver metrics, we make a new shortcut n3-mybestinstance, which picks the right shape/processor family etc for yah.
As a Googler: take VM rightsizing recommendations - "save $X because you're underutilizing this machine shape" - and extend them to encompass this by including VM-family swaps based on underlying VM metrics? :)