Duo Hero Mode
Single Hero mode is becoming the "main" way of playing Heroes online it seems. Every YouTuber I come across strictly makes guides and tier lists ONLY about single Hero mode. When they talk about Heroes and Spells, they rate their usefulness exclusively on how it performs in Single Hero Mode.
Personally I think that's alienating a lot of what Heroes has to offer which a 2 Hero mode would solve. I think Duo Hero mode would have the best of both worlds. You don't need to micro 8 Heroes at a time like in Jebus Cross, but support Heroes would have a place to shine.
It would be nice to have a "Duo Hero Mode" as an alternative option in the future.