M Mount Wide Angles and RAW - X series

The filter plays a role, but if you use a more telecentric designed lens, edge problem goes away, so ultimately, it is a micro-lens fix requiring a completely different sensor as used in Leica M9. The new Fuji (retro-focus designed) 14mm will have much better edge performance despite having it's peripheral rays go through that same "thick filter". It comes down to registration distance and lens design.

However, I don't understand how you can say that Fuji uses same sensor as in the cameras that you've listed. Those sensors are Sony std Bayers-style. Fuji's X-Tran has completely different RBG layout; not identical sensor.