> As a technology, ICE is pretty much close to its peak. It's very hard to imagine significant improvements in ICE as far as efficiency, weight, and power output goes

What makes you say that? Jet engine manufacturers are constantly making improvements, and one of the biggest recent breakthroughs has been around using proprietary alloys in the construction of some parts to make them lighter and able to operate at hotter temperatures, thus increasing efficiency. I'm not working on any engines, but from a layman's perspective I don't see why there couldn't be material science improvements made to combustion engines.