There's another fast 28mm alternative on the market - Leica Q.
It's as sharp as 50/1.4 ZA and FE 55/1.8 according to DPreview studio scene samples at f/5.6. With distortion correction
embedded into DNG profile, Q shows less distortion than Sony's 50 & 55mm lenses uncorrected. Which is still striking for a "brick wall" scene. IQ overall is amazing right from f/1.7 keeping in mind the image processor corrections (aberrations and distortion).
What bothers me is poor optical correction for distortion which becomes obvious in portraiture. Embedded profile doesn't help in this scenario. I'm yet to see a half body portrait that won't showcase twisted body parts. I know it's tough for 75° FOV, but it's a priority for me above the acutance.
In addition, Leica's reluctance to post MTF and distortion graphs make me pause and contemplate over the use of Q for my shooting style. I had high hopes for this camera.
28mm f/8
Another gripe I have with Q is iso12500 quality. It's below acceptable level for night time photography. Red channel is falling apart at this level of sensitivity with highly inaccurate color gamut. Canon 6D with 28/2 ZE will do a better job than Q in this regard.
I'm looking at Sigma now and hope they release 28mm Art lens soon.
28mm f/1.8