Larger displacement will also deal with more parasitic friction losses. Can't have it any other way. More pistons = more displacement = less stress per bore and also added friction per bore.
Higher stress motors will work, with added work and engineeering in tribology/oils and their additives, and with better, newer materials/alloys and metallurgy to handle additional loads. But it's going to take time, failures, and lots and lots of beta tester miles before the bugs all get worked out, me thinks. Will reference fuel be an issue again in fuel pump designs? ;-)
Bosch has backed off on the pressures the CP4 series of HPFP's operate at, letting exhaust treatment do the additional clean up. They have also, in some cases, gone to a smaller bore and a longer stroke to make the fuel volume per injection cycle on their CP4 series pump, effective in 2012 in the VW passat CKRA motor, also went with less expensive solenoid injectors, versus ceramic piezo injectors, that can crack and contaminate the fuel, like in when bleeding fuel lines on the high pressure side. Another reason to not run your diesel with HPFP out of fuel or get down less than 1/4 tank of fuel in the tank, taking on air and cavitating is bad bad juju for these pumps.
All of this translates to the V6 TDI motors in VW Touaregs, Audi Q7's and Porsche Cayennes series of tow vehicles in diesel, as well as the European V8 4.2 TDI not seen state side, or the monster V-12 they shoehorned into an Audi Q7 out of their 24 hr LeMans/ 12 hrs Sebring racing series motor. So the technology does flow down from racing.
