I think, above all else, that the new game should be able to boot up and play relatively easy on any desktop/laptop/etc. that has come out since CMBB was introduced. (Heaven Forbid every computer enthusiast out there rifling through the new computer upgrade/soundcard/graphics card trend who wants more, MORE, MOOOOOORE.)
The main ingredient that makes CM so great to me is that it's pretty damn easy to play on most notebooks and computers right now, WHILE INCORPORATING all the DETAIL and TACTICS that beat out any other strategy game on the planet! If the new engine is worse off than that durned Soldiers Heroes of World War II system SNAFU, I don't want it. Simply too slow and painful on the engine.
Accessibility for the current and older model computers, same attention to tactics and unit detail, maybe more ATTITUDE and PLAYER RANKINGS as far as kills/medals whatever, but, finally, the BFC stamp. You guys can do whatever you want and it will be awesome, but just make it easy for the next generation of middle and lower classes to boot up without a hitch and sink their claws into it.