Here are the first answers from the develeoper mail list:
No, it should work in any Linux distro where the requirements can be
met. Requiring people to install a different distribution than they are
used to would be a barrier to entry.
If there is a problem on a particular setup we want to know about it, so
we can investigate. If the build instructions don't cover a particular
distribution, we want to know about it and improve the documentation.
The only thing that may be problematic are really old releases, but
16.04 is certainly not too old.
I test installing the dependencies from the package manager, and then
downloading the KiCad source and compiling it on a clean 16.04 machine
every day and have been for a few months.
If they start to fail, I'll poke the list.