I can't find a reason why I'd prefer this option to whats already out there as a UWA option.
A UWA typically is used for large DOF and sharpness, so the f2 is not necessary.
This 16mm is not that wide, I run into FOV limitations even with the DA15ltd. (can't move back anymore unless I phase thru walls or can fly

)
Some may need it for unique low light+confined space+tripod not-allowed venues/work.
I just don't see it happening too often for most general photography.
Even in palaces/churches/etc where a tripod may not be allowed, I'd still choose to use ISO400,800 + enough DOF and sharpness with a f4 or f5.8 and brace/rest on some bench/wall or something.