Given the somewhat inconsistent HiDPI-support in a lot of the sorts of tools you need to be able to use in coding, choosing to use a 4K monitor is brave.
You can get it relatively consistent, but will still end up with a few older applications rendering at native resolutions (sometimes partially, where the text is fine but icons are too small).
Most distributions also don't offer any universal way of configuring DPI scaling. I think Ubuntu does, but last time I checked they were almost alone in that.
Like contemporary Linux has HiDPI support in the same sense Kdenlive is a video editor. It's technically true but leaves a lot to be desired.
Really anything rather than a thing that has only drawbacks.
As far as readability goes... can't see a difference with monospace text, maybe even worse as fonts tend to be thinner and need adjustments. Maybe a little better with proportional text on websites and documents.