I think it would be cool if there were certain global events that happened while playing at certain times in the game and better yet they could happen randomly since people complain about there not being enough random things and not enough annoying abilities that happen. There is a lot of room for creativity here so if you have something you can think of that would be truly intense or super annoying or whatever post it to receive feedback... here are some events I thought of...
A drought that happens that makes it so that you can't buy any Food capacity upgrades for 7 minutes and all heros regenerate mana as if they were rank 1 during that time.
A super tornado that spawns and will suck every building into it unless you buy an expensive ( Individual or team upgrade to counter that ) And it also does massive AOE damage until it's destroyed or just small AOE damage until it expires.
An Event that stops all normal spawns because you have to go on a secret mission of some sort
An event that stops all normal spawns for a certain period and replaces them with more Intense spawns
An event where a meteor lands in everyones base and starts to do AOE damage and when its attacked it breaks into smaller pieces and doesn't stop doing damage until all the pieces are destroyed
The point behind these events is to create a higher sense of urgency. I think that if this were to happen there would need to be some sort of announcement in game like a minute before it happened or just an event timer so that people at least knew like a minute before it was going to happen. And these events would probably be restricted to the higher difficulties but I really think there is a lot of room for creativity and a chance to expand on an already fantastic game