@popey As a non-technical user, I think that CSD apps and the eventual removal of headerbar patches (not sure if it’s already happening in 18.04) on those that usually ship by default in Ubuntu (as they are no longer necessary in GNOME) are a more drastic change for Unity users than MATE apps, hence my suggestion to use them, including Caja.
I do get that this still represents a big change, but long term, as GNOME continues to evolve, I think it’s best for Unity7 to stick to usage paradigms of its pre-CDS era, and MATE represents that.
I’m using all Ubuntu MATE default apps in Ubuntu 16.04 with Unity at the moment, with the exception of Caja (I’m using a patched Nemo instead) and everything feels more in line with the post-13.04 design of Unity7, and so everything looks more consistent, like it was in 14.04.
@dale-f-beaudoin is this going to be available for testing? I’d suggest simply include Ubuntu MATE’s selection of default apps (includes VLC as the default video player instead of Totem, for example).