I think the otto/miller/atkinson cycle has a much better probability of making a comeback, especially with the proliferation of this thread's topic.
Some of the hybrids on the market are using Atkinson cycle engines, and Mazda has had a couple of non-hybrids that supposedly use it as well.
I cannot remember many of the details, but back in the late 70s or early 80s, I remember a camshaft manufacturer (Cragar?) coming up with this intake cam design that would leave the intake valve open during a small portion of the compression cycle, thereby expelling a small amount of the air/fuel vapor. It resulted in improved mileage, and a slight supercharger effect as the forced air/fuel vapor pushed itself back into the intake manifold. I don't think it went anywhere.
I was just thinking. Caddy had that cylinder disable system in the early 80s 8-6-4 (?) A big bust. I kind of think there were/ are a few that followed (much more recently).
Honda has had VCM (Variable Cylinder Management) for several years now in some of the 3.5L J-series V6 engines. I am pretty sure they first used it in the Odyssey minivan a couple of generations ago. It can disable two or three cylinders during highway cruising to assist in gas mileage. Others have done this also, so it finally is a viable idea. Caddy's failing wasn't so much the concept (it was a great idea IMHO), but the technology to make it happen was not advanced enough, and therefore too troublesome to be reliable.
My 2.3 litre Merkur XR4Ti has been turbocharged since 1988, they were making them back in 1985.
The engine used in the Mustang SVO and the Turbocoupe both had intercooling, with the intercooler sitting right over the turbo and exhaust manifold. Why they didn't intercooler the Merkur is beyond me. They were already getting into the Sierra Cosworth over in Europe, they could have used that setup. The SVO and Merkur both ran an 8-bit ECU, with the SVO set up for more power. The turbocoupe had a 16-bit computer which can be retrofitted into the Merkur by changing some of the pin-outs. Turbocoupe ran a serpentine belt, Merkur used a pair of belts for the water pump, PS, alternator, with the AC driven off the water pump pulley with a single belt.
There was an aftermarket intercooler for the XR4Ti, but it required running a lot of ductwork out to the front of the car, which increased turbo lag even more. I suppose a better alternative might have been to hack a hole into the hood and add some sort of scoop to cool it, but that took the modifications beyond the abilities of the typical garage handyman.
I thought the Sierras used the Cosworth V6, and not a turbo...or did that come later on? That was one complaint I had read about the Sierra/XR4Ti when it was first imported--they left the nice Cosworth V6 in Europe and stuck us with the 2.3L turbo when they decided to import it to the US.
It's just a shame it was the least reliable car I had ever owned--it was a blast to drive...when it ran. Had there been lemon laws, I would have won big-time, as the manual transmission was never right in it. Why they didn't use the Turbo Coupe's Borg Warner T5 is still a mystery--that made no sense to me. I felt it had the better ratios (better suited to the turbo's ideal RPM operating range), it had shorter throws, and I'm sure it had to be a lot more reliable than the original Merkur 5-speed. At one point there was an aftermarket kit to swap in the T5, but it was pricey (as it included a new T5 transmission).