I believe that AoE3 still has a lot of untapped potential, it doesn’t need a replacement just yet. When the time comes for a new installment to “replace” AoE3, I would like for it to focus on the following:
Much better naval gameplay. AoE never has been very good at dealing with navies, I believe there is a lot of room for improvement here with a new engine. It’s also historically relevant as this is the period of the “Great Navigations”.
A Revolution revamp. The entire revolution mechanic is such a cool idea, but it’s very poorly implemented. If I had the chance, I would love to scrap everything and start over with a clearer and fresher goal in mind.
More coherent allies. Because of content creep, the different native civilizations are very uneven. Euro and African allies have much better and more interesting features than their Asian and American counterparts. Also, I would have european and asian allies being actual natives, instead of “Royal” or “Religious Sites” for consistency.
Some sort of World Conquest mode. It think it could be cool for a dynamic campaign-ish mode where you can pick an Empire and try to take over the world, conquering territories and managing resources on a macro-scale. It could be online or offline.
Different terrain types with different effects. In order to make maps feel more unique and force players to use different strategies, I would like to see stuff like Snowy or Desert terrain making it impossible to build Farms or muddy areas that slow units down.
Finally, my starting roster would be:
With more civs as DLC down the line.