Tamron looks to be trying to create an f/4 version of its well-regarded f/2.8 standard 28-75 mirrorless zoom. The f/2.8 version is already surprisingly small and light, smaller than most photographers thought possible for that aperture. It would be interesting to see how much thinner such a lens would be designed to be a stop darker.
Interestingly, the patent application shows that the closest embodiment to the f/2.8 lens already on the market would actually be significantly longer, at about 15 centimeters in design length, versus the lens you can buy today that is only about 12 centimeters long. Both lenses appear to have 16 elements.