I don't know because I haven't bought one, but I do know they run their own distro called Pop_OS[0] which is improved ubuntu (with likely impeccable support for their hardware).
That in-and-of-itself is a pretty impressive investment to me, but I would probably take it off and put arch on it. Honestly I am not too worried, it seems like I can actually call them for support/file bugs/ask for technical help if I actually came across an issue -- surely someone over there knows something if they want to maintain their own distro.
Thanks for the comments on this, I'm generally skeptical with these things... my only linux desktop is currently running Elementary, which I've liked a lot, but nice hardware support will be great. Still running a late 2014 (iirc) rMBP for my laptop, may swap out late next year or the year after.
I'm tired of the stuff Apple pulls, so would be nice to see a good/supported linux distro for hardware. I've been bitten too many times trying to maintain Linux on a primary desktop/laptop (hackintosh has been easier for me).