there are a couple of small things i have been thinking of as i have been playing:
-Small crown cost (or possible "treaty" like negotiation of resources) to do a small "ally" agreement between to players.
*(this one seems like a decent sized task without knowing how your code is written and might be nice in the long run for some player diplomacy as well)
-send friends units as well as resources. (or possibly buy mercenaries from another player.... something to transfer units around as well. but the second way prevents people from being rushed to late game when they just started.)
-History tab (like social or profile) that just gives a one line summary of what has happened in the last, say 24 hours such as:
"[time stamp] [insert player name] attacked you at [time] and [outcome of fight]"
"[time stamp] [insert building] completed"
"[time stamp] You attacked [insert player name] and [outcome of fight]"
-Banking system to store some resources (at a cost). I envision a 10% cost to store it to the bank but if someone were to attack you and defeat you they could only steal say 50% of the normal amount they would steal if it was deposited and resources in the bank would cost 125% of the resource space it would normally cost. in this way if you get attacked a lot you could potentially save some of the resources but you also wouldn't be able to hold as much as you would normally making a plus and down side to both choices.
-advanced tooltips! i have seen so many tooltips that simply state things like "improves range and sight", "improves attack power" etc... I, and probably many other experienced gamers, want to know the specifics.... how many points does it mean.... what's the actual numerical impact of the upgrade.
-as stated by another post, i have to reiterate because i do it A LOT!!!! please please please allow the escape key just close the menu that is currently open and deselect who you have selected and if no menus are open and no units are selected THEN open the menu screen.
just some suggestions but i don't know your code or how easy it would be to implement them in game but just some useful things that maybe can be turned on or off in the gameplay menu for the more experienced players.
in closing even if these are not something that gets implemented, thank you for at least reading it !