Publisher 2K Games released the PC/OSX/Linux system requirements yesterday while the actual Linux port continues to be done by Feral. To not much surprise, only NVIDIA is listed in terms of the Linux graphics requirements.
A NVIDIA GeForce GTX 650 is listed as the minimum requirement while a GeForce GTX 960 with 2GB of vRAM is what's recommended. The page explicitly mentions "AMD and Intel GPUs are not supported at the time of release."
Aside from needing NVIDIA graphics, the Linux port recommends having at least an Intel Core i3 3.3GHz CPU, 4+ GB of system memory, and Ubuntu 14.04.2 or SteamOS.
Under Windows, the system requirements at a minimum come down to a Radeon HD 5770 or GeForce GTX 460 while they recommend a Radeon HD 7970 or GeForce GTX 770. On OS X, a GeForce GTX 700 series or AMD Radeon R9 series graphics card is recommended.
More details via support.2k.com. Given that XCOM 2 is powered by Unreal Engine 3, hopefully in the near future this game will start playing nicely with the Mesa/Gallium3D drivers. If there is an automated benchmark mode for XCOM 2, I'll have up plenty of Linux GPU benchmarks shortly after the title's release.