The Nexus model chooses a manufacturer and then works with them to create the current year's creation. I'm not sure Canonical has enough resource or leverage to do that.
That said, I'd love to see an Apple-esque model where I could point to 3 laptops each year and say "large, medium, and small" and know that they would work completely with zero fussing.
Maybe Canonical could start down this road by refitting their devs with new laptops on an annual cycle and saying, "these are the laptops we will be using this year."
I'm a NetBSD-to-Apple switcher (circa 2003) who has a fair bit of ambient familiarity with Ubuntu as his auxiliary OS. I don't run any proprietary system beyond what comes bundled with OS X nowadays. I could switch to Ubuntu for day-to-day work and be perfectly content.
I can say that the SOLE factor of why I haven't has everything to do with not finding a rival to my MacBook Air 11". Part of that may be there simply isn't a comparable machine. But part of that may be that the hassle of searching for alternatives is simply too great.