Well if that is the theory then Honda, Toyota will be the first to discontinue the navigation system, because they are the ones who follow Keizen, and when they see Diminishing returns they will axe all their navigation models if they think they will be on point of diminishing returns.
Considering,
a. All platforms of GM are/ will be worldwide, there will be always need for some ammenity/ equipment in one market compared to the other. Let us say for example 6-speed manual in a Epsilon. This is certainly going to be a possibility in European bound sedans. So the development money is going to be put forth, what is needed is minor retooling while manufacturing for USDA.
b. Take a look at Honda, they have one 6-speed manual transmission which they put in every darn car they have. I am sure if GM does that, it will at the most need two good 6-speeds. One for low performance vehicles, other for higher performance. As a matter of fact they can just make the Hi-po transmission "heavy duty". How much will that be for development and design, considering the expertise they have to simulate the real world conditions in modeling, I do not foresee any serious development dollars going in the manual transmissions. Or heck, give it to Tremec, Aisin or Getrag and ask them to meet the specs and let there be a "healthy competition".
c. Again Navigation. They put Navigation in the TrailBlazer..... I am sure Trailblazer was not tooled for that considering it has the 1990s corporate radio system. They cannot do that in the Malibu? Wonder how many of those navigation Trailblazer did they sell. I am seeing more and more cars with navigation systems. And many prefer in dash compared to the Garmins or Tom Toms. I am sure they can sell more Malibus equipped with navigation than the Trailblazers.