Gentoo on HP t520, one year later
The little thin client keeps chugging along. While I often do wish for four cores instead of two (like in those pcengines devices ) regular updates are very manageable (with major offenders being llvm at 4 hours and gcc at 5). I pruned the kernel config to the bare minimum so it does not take long to build. I intend to stick with the current longstable kernel branch (5.4) for the forseeable future.
The world list has grown slightly, with some replacements here and there (parole for audacious) yet I managed to shave some dependencies. Gtk2 and Python2 are gone now, fully replaced with gtk3 and python 3.6. Xfce finally got the 4.14 stable release and it works very well.
The system takes about 5GiB of disk space (including 1.5GiB for a single copy of kernel sources).
Overall, I am very happy with the setup.