I wonder what the current state of this is? Any distro that supports very high ppi as of today? I have read that mageia offers support, but I wonder if that is truly the case? i find it strange specially because the most relevant DEs apparently don't work well yet?
As Linux uses X11 to do graphical rendering, this question is really about whether X11 supports it.
The answer is yes, X11 supports arbitrary sizes. One example with 4K HD is here.