LaBoule leaked some information about the racial abilities. The Necromancer's counter increases when someone dies on the battlefield, on either side. Well, we kind of knew that (but for me personally, it was news, as I missed some details). The Human faction's counter will increase when morale triggers. However, it's not clear exactly how. Either only from positive morale among their own troops, or... Anyway, I don't know. But that's not all...

Plus, humans always mourn the fallen. Shouldn't they receive some reward for that?

Interpret the hint as you wish. The Demon faction's counter will increase from something probabilistic, like luck or morale. It might also be from abilities that are also tied to probability (for example, stun). But it's not yet clear exactly what triggers it. What do you think about this?

They might bring back the Gnolls, because Orcs aren't the only test subjects for mages; it's quite possible that their faction will include other beastmen, besides Centaurs.

The Orc army doesn't have beastmen. Centaurs are not beastmen. They are born from the union of hellish nightmare horses and humans. The same as half-demons, half-humans.