I have less concern over this approach than I did have, thanks to above posts from @Adrian_Joachim and @Deuce. The additional height should be very minimal, particularly as your own research suggests that it may be possible to accommodate the ULP switch within the existing case. If so, it stands to reason that only a little more headroom is needed to make it a comfortable fit. I think that if an ULP compatible case was made it would be very difficult for the average person to tell it apart from the current design without comparing both side-by-side.
I understand that the “open” aspirations of the framework hardware do not extend to CAD drawings of the chassis, obvious when you think about it as they don’t want to do the job of clone manufacturers for them 
. There are however threads where the case drawings are reverse engineered, such as that here.
Another user is looking at a deeper, more rugged chassis possibly with headroom to accommodate “mechanical” keyboard module. However the stated goals of the project require certain compromises in aesthetics, mass and dimensions, whereas this thread agitates for the chassis many of us feel Framework should have as standard.