According to the 2020 Sneak Peak, there is going to be a revamp of the 4 Seasonal Events which will include heroes etc…
Whether there will be new heroes for ALL 4 seasonal events, nobody knows 
Nothing has made it to Beta that I’m aware of yet so… Nothing Concrete.
Link to 2020 Sneak Peak by SGG Staff:
Start of the Most Epic Empires Decade Yet - 2020 Sneak Peek!