I've run Linux command line tools and GUI tools using Termux and a random X11 app. . It already works, just not with stuff requiring root permissions (no wireshark etc.). Apps like https://play.google.com/store/apps/details?id=tech.ula do it through VNC instead.
What I found to be the most limiting factor isn't the OS, but the tiny screen and the lack of good input methods.
Funnily enough, Samsung ran trials where their Dex mode provided a full Linux GUI when plugged into a monitor/USB dock, but that got killed off. Now Dex is back to being an Android desktop environment again. On the plus side, Dex now also works on tablets without being docked, so I guess that was worth it for me.
