What Vehicle Needs A Fourbanger Option?S

One of the easiest ways to downsize fuel consumption is to downsize the engine, as Toyota demonstrated with their four-cylinder Highlander. Though some may worry this is the start of another Malaise era, we'd point out that turbocharged Audis are quite desirable. Cadillac has already announced that they're into it if we're into it, and they have the popular Ecotec engine to back them up. So what other cars should get inline-four goodness?

Is Ford talking crazy when they mention dropping a four-cylinder Ecoboost engine in the F-150? Should we have four-cylinder trucks (again)? What about little diesel engines? We'd love to get the small diesel option in the US Cadillac CTS Sport Wagon. Where does it make sense? Where doesn't it make sense? Where is less more? What vehicle needs a fourbanger option?