The Xiaomi Mi Developer Conference (MIDC) is underway and an incredible prototype smartphone with a mechanical zoom lens has already been revealed. Xiaomi is also apparently planning on becoming the number one smartphone brand in Europe and will recruit a whole new army of engineers to help with that task.
https://www.notebookcheck.net/Xiaomi-reveals-prototype-smartphone-with-single-mechanical-telescopic-camera-and-plans-to-take-over-Europe-with-the-help-of-5-000-new-engineers.502295.0.html
Judging by the size of the front element, this doesn't notably collect more light in total than Panasonic CM1...Moreover, it's a zoom and that's a prime so by light gathering alone a prime would no doubt be more space efficient than a zoom.