I think you mean 2017 ATV4K1. There wasn't any new ATVs in 2018.
The ATVs are one of the harder devices to guess when the next one might be out.
While it isn't an exact science, there is a little bit of a pattern. Not counting the original 1st gen from 17 years ago, every other model has been released in pairs, with a long wait in-between. The first one of the pair (2 out of 3 times) has been a significant change over the previous generation, and the second one of the pair has been a performance increase (3 out of 3 times).
2010 ATV2 New design and UI
1.5 years later
2012 ATV3 Same design and UI as ATV2, just with 1080p and faster chip
3.5 year break
2015 ATV4 (HD) New design and UI
2 years later
2017 ATV4K1 Same design and UI as ATV4, just with 4K and faster chip
3.5 year break
2021 ATV4K2 Same design and UI as previous pair, and a chip that was only slightly better than the 2017 ATV4K1
1.5 years later
2022 ATV4k3 Slightly updated passive cooling design and same UI, larger storage option and faster chip.
Again, not an exact pattern, but maybe enough to make a better educated guess.
If this holds for another round, it won't be until around the Spring of 2026 before Apple releases a new ATV.
But, there are things that might Apple break the pattern, one being that it kind of already broke it with the 2022 ATV4K3 being fanless.
Maybe Apple might stick with what ever chip makes most financial sense, and upgrade sooner. An example is the A12 in the 2021 ATV4K2, it wasn't really that much of an upgrade over the A10X in the 2017 ATV4K1.
One issue that may prompt a sooner than later upgrade from Apple is the fact that the A15 in the fanless 2022 ATV4K3 has bad thermal throttling issues for gaming, making it perform worse than the A12 in the ATV4K2 in some situations. Maybe Apple might use a 3nm A17 for the ATV4K4, since it would run faster and cooler than the super hot A15.
It does get really hot too, some people have been resorting to active heatsinks to cool it for some games:
View attachment 2243929
So, what does all that mean for you:
If Apple doesn't break the upgrade cycle pattern listed above, it could almost 3 years until the next ATV.
I wouldn't wait, and just get one now. They are great devices, and even if you plan on playing games on the AV4K3, a lot of games runs just fine without a fan.
If you don't play games, you don't need the Ethernet, and you already have an ATV4K2 with thread, maybe consider finding a good deal on the 64GB version of the ATV4K3.