I agree with you on the principle: there is lot of effort going into lots of distro, if they were focused only on one sure we'll have a really fine tuned system. Unfortunately with Volumio we use a very peculiar mounting mechanism (squashfs + overlayfs) and we based the whole partitioning on that. I fear that just an override script won't be enough to customize armbian enough. In any case I'll give a try.
I understand you are against reinventing the wheel, and I agree on this, but some practical reasons and peculiarity of all distros are a showstopper for a "universal" OS, IMHO