The new 40mm Zeiss Batis (for Sony) is being announced next week, and is widely leaked. Pretty big lens, and that's 'only' for FF35mm.
To hit the numbers (MTF, Distortion, CA) Zeiss/Sony are having to go for a Distagon formulation, which is not small. (interestingly the Otus range are called 'Apo Distagon' by Zeiss, so them too). Basically afaik, Distagon types get the light to enter the sensor cells more head-on, than it otherwise would with Biogon type formulation.
I too am in favor of cheap compact lenses, (who isn't?!) but we all have to recognise there is a trade off. I own the Plastic 50/1.8 for Canon and used it on a 5DSR at times because of its aberrations and corner funkiness. Nobody is saying Fuji will release a rubbish lens, just reminding to be aware a compact ~40mm equivalent will be a step below one not formulated under such design constraints. You (and I) may feel the trade off is well worth it.
There are plenty of pancake lenses out there, from Canon's 40mm (amazingly compact, super cheap, but poor corners and very strong field curvature) to Large Format even - Nikkor's M View Camera series. It's great they exist. No debate about that.