Congrats, you got the best GPU that was released in this decade without knowing it!
I would OC it heavily as others have suggested. Maybe get a custom waterblock or a custom cooler like the Artic ones if noise is an issue. I wouldn't invest in a new GPU at this stage.
If you want to go to 1440p and above, I'd say upgrade. If off-again, on-again 1080p gaming is your primary usecase then I wouldn't even be sure if a GPU upgrade next year would make a ton of sense since I don't expect a dramatic increase in visual fidelity.
I'm going to upgrade pretty aggressively because I'm moving to a 165 Hz 1440p monitor from my current 1080p 144 Hz one, and even today a 980 Ti can't sit at 100+ fps stable on 1080p at some AAA games like Witcher 3 or Crysis 3. So even if I had my old monitor, I'd needed to upgrade next year anyway. Now you add 1440p and it's even more aggressive.
But far from all people have such a bleeding edge preference and your needs may actually be covered by your current GPU. People sometimes over-upgrade over what their actual needs are. Be honest with your true needs.