AOE 4 need to store replay of game that have been played in PC or they can make unique number ID of said game so it can be access by someone else easily like how they do it in DOTA 2.
Observer mode need to include ranked matches of high skilled player so newer player have the ability to see how to play better & know more about people in highest level. so then they idolize them and want to improve to be like them. and also add tournament too. it will be great if caster can be heard in observer mode, again just like in dota2.
much of the things that make RTS interesting is the ability to watch other people game that plays in highest level of play