Are there any risks involved in installing DWM in DOM0, even if everything else remains unchanged? Perhaps I’m too fixated on the purity of the Qubes OS architecture, but as I understand it, DWM will generate more trusted code and more packages. Are there any risks associated with this, aside from configuration issues?
Window borders with distinct markings are important. QubesOS tests Xfce, KDE and i3 on OpenQA, so we know that to some extent, they are working. There are some bugs on i3 related to border coloring appearing the same as dom0, which nobody has been working on. What I mean is, DWM is not tested, we don’t know if it works in all cases, and you will be trusting a third party for code that you will run in dom0.
If you just want a stacking window manager, go for something shipped by QubesOS repos, which is i3.