Chromebooks are the answer to the question: “What’s the point of an operating system if I do everything through my web browser anyway? Why not make a computer that just opens a browser?”
Your choice of distro is probably less important than your choice of DE. Chromebooks vary quite a bit in their specs–many are low-end hardware, but some are quite impressive. With decent hardware, I’d recommend Mint with Cinnamon DE as a good starter. For lower specs, you could try Debian with XFCE.
All this list does is prove that the rooting community is indirectly contributing to the mainline distribution by innovating where Google and OEMs won’t bother.
Also, stock Android still doesn’t let me customize my hard/soft buttons, so I’ll be sticking with LineageOS.