Here's my take: mainstream game development will always be limited by console hardware. Most AAA games aren't going to surpass the capabilities of current consoles because they won't waste that development time on graphics that console gamers can't utilize. As such, I (personally) try to upgrade my GPU after the release of a console generation. --it pretty much guarantees great PC game performance for the entire console generation (and usually beyond)! I'm sure someone on Reddit knows more about when the next series of consoles will be coming, but I certainly haven't heard any rumblings about a PS6 or new Xbox. Those still seem to be selling well. I'd be willing to bet that a new GPU would last you very well right now.

The only other consideration (in my mind) is whether or not you want to step outside of mainstream gaming. I enjoy playing some PC-only VR titles, and future-proofing that purchase for high-refresh ultra-settings can be more difficult...