Acer XG270HU uses FreeSync which is not supported on NVIDIA cards. Also, I think an Acer TN panel will be a downgrade coming from a BenQ TN panel, image quality-wise. If you go TN, go with some other brand than Acer. I hear the Asus PG278Q actually has pretty good image quality for a TN panel, and it has GSync as well. For a little bit less $, there's BenQ Zowie XL2720 which is also pretty good for a TN, but has FreeSync instead of GSync. I think you'll want to pay the extra for GSync, it will make a big difference when running 1440p resolution on a GTX 1080.
But I would upgrade more than just the resolution. Going from 1080p to 1440p, you're going to feel underwhelmed if all the other specs are the same, considering the amount of money that upgrade is going to cost. I'd go for an IPS or VA panel. Here are some VA/IPS GSync screens:
AOC AG271QG 27" 2560x1440 AHVA 165Hz
Acer XB270HU 27" 2560x1440 IPS 144Hz
Acer Predator XB271HU 27" 2560x1440 IPS 165Hz
Acer Predator Z271UV 27" 2560x1440 IPS 165Hz
ASUS PG279Q 27" 2560x1440 IPS 144Hz
ViewSonic XG2703 27" 2560x1440 IPS 165Hz
Finally, I'm not convinced the graphics card needs more pixels. 1080p @ 144Hz is plenty of work for a GTX 1080, much of the time you're not going to hit anywhere near 100 fps on maximum settings in graphically demanding games, even if your CPU doesn't bottleneck. What is your CPU by the way? And what are the rest of your specs? When asking for advice about
any upgrade, it's always a good idea to list all your components and peripherals just so people know what sort of setup they're dealing with and if the upgrade makes sense.