My understanding of "modern engine" is the introduction of direct injection and predominantly timing chain/variable valve train, engines. Throw in a turbo too if you like.
This^^^ to me has been the advancement of the modern engine, and when people mention it, they talk about the problems/hiccups we are seeing along the way of it's maturation. Valve coking, misfires, LSPI, timing chain stretch/premature wear, oil consumption, soot, fuel dilution, shorter oil change intervals, new oil certifications with different standards than in the past (used to combat these things).
That's what I think of with modern engines.