Looks like my wishes for a small, affordable, f/2.0 rectilinear ultra-wide-angle lens have finally been answered! Venus Optics just announced such a lens in the Laowa 7.5mm f/2.0 for M4/3!
The Laowa 7.5mm f/2 MFT is the Widest f/2 rectilinear lens ever designed for Micro Four Thirds Cameras. Despite the extreme specifications, Venus Optics has successfully minimized the weight of the lens to a merely 0.37 pounds (170g) and 55mm long. The extreme 110 angle of view, ultra-fast f/2 aperture and featherweight make this lens an ideal option to pair up with drones for aerial photography. It also gives photographers a fast and wide-angle option for low-light shooting as well as landscape photography.
If it performs reasonably well and is affordable, which it should be, then this will be a fantastic new option and fill the only hole we still have in the M4/3 lens line-up.