FPS boost seems to be problematic with many titles (e.g. some titles introduced gamebreaking bugs with FPS boost enabled) so the support ended. What I really wished they would intensify is Res-Boost for older titles. Especially the x-enhanced titles looked phenomenal. There are so many xbox 360 and xb1 gems that would really benefit from just doubling the resolution ... but they ended the complete BC program as far as I understood.Everyone knows that or should know that.
Remember, Microsoft had to get permissions from the game developer/publisher to put them on Backwards Compatibility and FPSBoost. When Microsoft owns all of the Activision back catalog, they can give permissions to include all those titles where as Activision did not. That is the main point. The barrier to getting permissions from Activision is removed.
I really hope that current titles with dynamic resolution systems will be much better equipped for the future.