Maybe not a single reference device, but there are fairly standard devices that are advertised, ship with, and offer support for Linux. The HP Z8 claims "Ubuntu. Certified and pre-installed." I've always run RHEL or CentOS on them and the company I worked for paid Red Hat for kernel customizations...so I figured there was comparable support. Yes, these are workstations, but HP says the same thing about their zbook. I've just never used those.

System76 manufactures computers exclusively for Linux. Dell XPS laptops are also pretty popular with Linux users. Thinkpads were historically, as well.

I would think you could get financial support for a few base models and enough widespread support for at least half a dozen hardware configurations.

https://www8.hp.com/us/en/workstations/z8.html