I really enjoy the idea of Heroes having different kinds of relationships and playing off them via game mechanics and I think that could be introduced into AOW4 to a degree.
For example, there is a game called Wildermyth, and they have 3 relationship types with different bonuses for each. Friend, Rival, Lover. They also have 5 different levels of the relationship that scale the bonus. Here are the bonuses from that game.
Friend - While next to each other they provide each other with armor protection.
Rival - If one's rival scores a critical hit, this character gains an increased crit chance and vice versa.
Lover - The lover of a character that has been struck by an enemy gets a massive damage bonus against the enemy that struck their lover.
I think it would be neat if we could have something like this, along with a few narrative events between heroes that could create these different bonds between Heroes.
It might lean a bit more into the Roleplay aspect than anything, but it could be fun to create an iconic duo like Gimli and Legolas if you adopt an elf or dwarf during your playthrough.
I'm even thinking you could expand the roster of relationships with premade heroes, I mean we already have free city rulers mentioning their sons, daughters, fathers, mothers, etc. So why not have a family of conqueror's with the matriarch or patriarch being the Godir in charge and providing bonuses for fighting alongside their family members!
Idk, I just think it would be something neat to add a bit of flavor to our characters and their interactions with one another.