Yes, you would need a new 4k player, and a 4k capable tv. I personally haven’t seen the value in upgrading until my gear dies. By then, 4k will be standard, and 4D will be the new hotness.
4D will probably feature liberal actors standing virtually in your living room, while they tell you that you’re responsible for all the bad things happening on earth. Very exciting! /s
I send stock footage up in 4K but have yet to sell any in that format. I’m thrilled to get an HD one. Most are small and medium size formats.
Why I bother sometimes is a good question. I spent too much time in TV production land and like making things with a camera.