I haven't tried a 4k texture pack myself, but it sounds like it would be amazing! Although, I can imagine that it would require a pretty powerful computer to run smoothly. I hope that technology continues to advance so that more and more players can experience the game in high definition.
Speaking of customizing your gameplay, have you heard of the True Survival Apocalypse Mod? It's an awesome mod that makes Minecraft much more challenging and realistic, adding things like thirst, hunger, and disease to the game. It's definitely not for the faint of heart, but if you're looking for a challenge, it's worth checking out!