I'd imagine we'd see it in the upcoming mini-BMW. I'm curious to see how it does. BMW is doing pretty damn good things with efficiency, and it would be interesting to see what they could do with 1.5L in three-cylinder form.
And when your aim is efficiency, who cares if it only has 3 cylinders anyway? The guy with the less efficient 4-cylinder car is better than the dude with the more efficient yet equally quick (read:slow) 3-cyl? Numbers are numbers, whether they be efficiency or performance, regardless of how many cylinders the powerplant has.