Thanks for the pings everyone. This project is still in the works, amidst a ton of other things we are trying to keep in check. My plan is to merge some of the smaller items into core while keeping things like buttons, header, and anti aliased font behind the feature flag for now.
I have made room for this next week and will begin sharing some more updates then.
What sort of issues have you run into with your theme and component work with this feature turned on or off?
This is just temporary for now as it is scoped to the upcoming changes feature being enabled.