X-A1 vs X-M1
I had the X-A1 (Bayer sensor) for 2 years, alongside with a X-T1 (same X-Trans II sensor as in the X-M1).
I've been using those two bodies together for portrait sessions and weddings, and if I look at my pictures, I'm totally unable to tell which picture was taken with which body.
I can only see a difference at high ISO (1600 and more). The X-A1 shows a little more noise, and more chroma noise (red dots). The X-Trans sensor is really good in high ISO department !
This doesn't mean the X-A1 is bad at high ISO, on the contrary, it's really good, but the X-M1 will be even better.
I heard that the X-A1 is better than the X-M1 for video. I never do video, so I can't confirm this, but it makes sense : the 2 first iterations of X-Trans sensors are known for not being good at video.