Drew

I´ve had mine for a week now.   It seems to be the lens we were all hoping for, it's very sharp wide open at 400mm and focus speed and stabilization seem good.  I had the Canon 400/5.6 L before and the 500/4.5 L.  The 500mm lens is the best lens I've ever had and worked great with the 1DsII I had at the time.  The X-T1 + the XF100-400 may not be there but  getting closer and hopefully the X-T2 will have improved tracking capabilities.  Overall I'm very pleased with the lens.
 
Here's a test shot with the X-Pro2 (pre-production model) + XF 100-400.  Lame subject ...but great feather detail.

 
I also think it looks quite nice on my GS X-T1.

#2- Hand held  1/20sec f5.6 ISO 200 @ 400mm
 

I ordered the new Fuji 100-400mm from Amazon DE last Friday and it was delivered this morning.
 
It was a grey rainy day today, really not great for photography. In any event, I immediately mounted the lens on my X-Pro1 and tried a few random shots around here. 
 
Very briefly, my first impressions:
Image quality is outstanding. Hand held at 1/15sec or 1/20sec is no problem, the OIS works beautifully, there's no motion blur, images are pin sharp. Auto focus is silent & relatively fast  -I need to still try this on moving subjects.  I'm doing a safari in Botswana in early April, it will be a good opportunity to test the lens properly.  
I've been waiting for this lens, so I could make a final decision on selling my Leica R APO 280mm f4. After a couple of hours of playing, the decision's been made, the Leica is going tomorrow...
 
Images are all straight out of camera Jpegs no PP:
 
#1- Hand held  1/15sec f5.6 ISO 200 @ 100mm