Also, I compared its size to the currently longest prime Fujifilm offers, the Fujinon GF250mmF4. You can see the results down below.
This is as accurate as it gets. But keep in mind that, while historically Fujifilm shares pretty reliable silhouettes of upcoming gear, the shape we see now is based on the current state of development.
The Fujifilm Fujinon GF500mm f/5.6 will hit the market only sometimes in 2024, hence minor design changes might still occur until its final release.
SmallRig Rotatable Horizontal-to-Vertical Mount Plate for GFX BHphoto* / Amazon / Adorama* / SmallRig* * denotes available for purchase at the time of this article, other stores to follow soon