Coming up very soon, late May 2018. It is the lens I was waitig for, for quite some time. I would still prefer a zoom lens in the range of the Canon 70-200 mm f/2.8 that I love for shooting details and for its versatility, but this lens is going to be even more amazing as for quality, since it will deliver medium format detail. It is also the first lens with image stabilization for the GFX, having a five stop-effective image stabilization system. It also features a linear autofocus motor that is both quick and quiet, and an internal focusing mechanism that limits the overall lens length during use as well as maintains consistent image quality throughout the focusing range. The lens is dust-, freeze-, and weather-resistant. Get the best offers for it from the link above.
FUJIFILM Fujinon GF 250 mm F4 R LM OIS WR tele-photo Lens (198 mm in 35mm format equivalent)