I vote that they instead offer a 4B12 variant of the cross, with a TD03 (or TD04, if possible). That's a 2.4L engine with a turbocharger capable of upwards of 400hp.
Then a proper automatic transmission that can handle the torque.
This vehicle has laughable gas mileage as it is. Unless you add a hybrid electric powerplant or two to supplement the measly and sluggish output from this 1.5L with probably really horrible head flow, don't expect to get 30mpg, even with a diesel.
The average driver's natural inclination to get more "power on demand" from a vehicle is to stomp on the accelerator. If the vehicle just doesn't have that oomph, it will eventually get up to speed, having consumed more fuel then necessary and not having accelerated any quicker.
The 3.8L N/A MIVEC engine in the 2006-2012 Eclipse GT has better gas mileage than the Cross. Actual clock with 10% ethanol pump gas @ about 400 miles a tank and cruising at an average of 2500-2800rpm (17.7gal tank). That's an average of about 22.5mpg.
The 1.5L turbocharged MIVEC engine in the Cross @ 10% ethanol pump gas gets 300miles a tank at an average of 3000-4000rpm cruising between highway and city (15.8 gal tank). That's an average of about 19mpg.
Someone tell me why that is? Ohhh yeah. Bad transmission, underpowered engine, and a whale of a body. And that's compared to a coupe that's engineered off the same chassis as a full-size Endeavor! With more than TWICE the displacement of the supposedly economical T/C cross.