- we rely very heavily on Launchpad - we rely on the hardware support and testing work they do - the Ubuntu userbase seems to be a bit more in-line with the kinds of people who will enjoy elementary OS (this isn't a technical reason) - we have some close relationships with Canonical/Ubuntu employees/developers

It's definitely a possibility, though personally I don't see it becoming feasible in the near term.

Kubuntu have already said that they will be using wayland and not switching to Mir, so you may want to talk with them, too. It doesn't seem like anything but stock Ubuntu will be using Mir.