There is an argument to be made that the shift to hybrid cars opens the door for a lot of engine design variations that did not work in the past. In a normal car, the engine drives the wheels directly which puts a lot of constraints on engine performance parameters (e.g. needs to be able to generate a lot of torque at slow speed, needs to operate over a wide RPM range, etc). Today's engines are a compromise to meet those requirements. If you decouple the engine from the wheels (as in some newer hybrids) and just use the engine as a generator, it can be run at its optimum RPM all the time, and does not need to be able to generate high torque.

So, I think it is feasible that we'll see some movement away from the 4 stroke otto cycle that is standard today, and some ideas that didnt work out in the past might work out better now.

Can I dream with a Ford Nucleon? ;-)

Another very interesting engine design is the Superball motor which was much hyped a few years ago, but nothing seems to have materialized:

http://www.youtube.com/watch?v=0CmGJucRDBk

It seems to use ceramic balls which have the same function as cranks in an Otto motor, which is probably a weak spot (much wear and tear). Otherwise the idea is elegant; an actual working prototype might be nice to see.