As a fan of the extended timeline mod I think more emphasis should be put on that part. I LOVED the barbarian invasion of Rome and the multiple heirs that would split your barbarian kingdoms. Ancient Rome in EU4 was similar to Ming. You just had to wait for Rome to attack someone and get a little weakened and then every bordering German nation declared on Rome all at once and it became a feeding frenzy.
The fall of the Roman Empire, fall of Charlemagne, the rise of the Tartarian Empire ("mongol" empire), the rise of the Ottomans/British/Russian Empires, rise of the USA and the rise of modern Prussia empire.
Extended timeline had some very interesting mechanics that don't exist in the regular game like the German barbarians, the development of cultures like french and anglo-saxon, large empire negative modifiers, the great schism, the great plague, mongol and Rashidun invasion, rebels that would take some of your provinces and become a separate nation and would have to win a war to become independent like the seljuks. building nukes to destroy development in a province, the space race, communism, European Union had an interesting concept but was always broken, and you had late game resources similar to coal like oil and uranium.
I just hope the timeline will be longer in EU5 than in EU4. A start date of 1356 And an end date near present day would be great.