Your TV will be fine for next gen.
It won't be able to do 4k 120fps, but not everyone can tell the difference between 60fps and 120fps, also only current gen and older games will do 120fps with maybe some indies doing it to, but I don't think it will be a big deal for most people.
I to have a mid range 2017 4k Panasonic, It was actually a stop gap TV, because my 2009 1080p Samsung broke, and I was going to get an OLED a few yrs later, but after using the Panasonic for a few yrs now I'm pretty happy with it, sure it does not have HDR and 4k 120fps ability but those things are not that important to me. They won't effect my enjoyment of the game.