While Legion won't include a big graphics overhaul like Cataclysm, the draw distance has been increased substantially, so there are new system requirements.
Operating System: Windows XP / Windows Vista / Windows 7 / Windows 8 / Windows 10 with latest service pack
Processor: Intel Core 2 Duo E8500 or AMD Phenom II X3 720
Video: NVIDIA GeForce GT 440 or AMD Radeon HD 5670 or Intel HD Graphics 5000 NVIDIA
Memory: 2 GB RAM
Storage: 45 GB available hard drive space
Internet: Broadband internet connection
Media: DVD-ROM drive
Input: Keyboard and mouse required. Other input devices are not supported.
Resolution: 1024 x 768 minimum display resolution
Intel Core i5-3330, AMD FX-6300, or better
NVIDIA GeForce GTX 750 Ti or AMD Radeon R7 260X or better
4 GB RAM
It's worth noting that setting the game to max and expecting 60FPS will now require a fairly substantial rig, particularly in busier zones. Dropping the draw distance a tad might be the easiest solution if you'd prefer the silky smooths to seeing what's going on in Duskwood from Stormwind.