So according to Fujirumors, the planned fast telephoto lens is "confirmed" to be an XF 200mm F2. Patrick over at Fujirumors has had a great track record as far as I remember, to me this can be considered to be 80-90% true.
I find this to be a little bit disappointing. As mentioned in my X-T2 reviews, wildlife photographers would be best served with a high quality 300mm F2.8 or faster, which will pair nicely with the XF2X TC to give a respectable 600mm F5.6 combination. This will mean faster AF and cleaner backgrounds for smaller subjects.
A 200mm F2 will yield a 400mm F4, which is a great addition for Safaris but not so much for birding. Oh well, one lens at a time I guess.