To run (let's ignore build deps for now) it needs dconf, desktop-file-utils, glib, schemas, python, ibus (you can disable it but it still has to be there, annoyingly), telepathy, a seat manager, pulse, polkit, eds, mutter, gtk4, and whatever fonts you want. If you want it to display on the local machine you'll need an xserver; as of now each of the apps can simply act as a client though (which is the capability they are discussing getting rid of).

I know this because I'm a packager...