Up similarly explores concepts of grief and mourning, so if the folks at Pixar can find a way to bring Carl Fredricksen, Russell, and Dug into the Cars universe, they could easily find some common ground to explore these mature themes.
Then again, even if we just get a chance to see the Up house flying in the background, that will likely be enough to drive Pixar fans wild.
Cars 3 will focus heavily on the legacy of the late Doc Hudson and the impact that his passing has had on Lightning McQueen in recent years.
With the upcoming release of Cars 3, the possibility of some shared themes between this franchise and Up actually makes a bit of sense when we look at the underlying stories of both projects.