Your observations tend to mimic my own. ETW is definitely MUCH more challenging in SP than the last few games, even with the AI in its current state. If the game starts with a nation without overseas provinces (i.e. Prussia, Sweden, Poland/Lithuania, Austria) it will probably be decently challenging at the start. Our old problems of massive initial expansion due to everyone conquering whatever is nearby with a 3 unit army is no longer a concern. With a decent rule system that allows for effective internal 'political' competition, the AI could well be enough to keep us occupied with fun ETW PBMs for a good while. Not all PBMs have to last 1+ years, after all.