Okay, I'll rewrite my ideas later, but only for the new races.
Added after 12 hours 53 minutes
As promised, in a different format:
Race -
Storm WarriorsStyle — Old Slavic architecture. Favorite magic — Air.
The image is taken from the mythology and culture of the Eastern Slavs.
The basic troop composition will be similar to the Alliance composition:
Swordsmen instead of Spearmen.
Archers instead of Crossbowmen, with crossbows as an upgrade for archers.
Nuns instead of Acolytes.
The elite units are different.
Thunderbirds and Rocs will replace Griffins.
Air Elementals will replace Radiance.
Bogatyrs will replace Paladins.
More details on them:
They should look something like this:

But the upgrade horses will have elements of incorporeality and will turn into wind in various places; meaning they are constructed from wind, but look like ordinary horses. Instead of the two abilities—charge and light mode—that Paladins have, Bogatyrs will have one ability. By activating it, the Bogatyr accelerates to incredible speed, turning into wind, and attacks the enemy with great force, passing through all obstacles.
Instead of Angels, there will be the good old Zmey Gorynychs, or as I call them, Eastern Serpents. They fly, have three heads, and are slow-moving. Ability — multi-target attack, like Cerberus.
Lore:
Actually, this nation was not intended for Ashan. In Ashan, such a race could be any followers of the Air Dragon (including the Free Cities of the East).
P.S.: Sorry for the image. Mods, please fix it as needed.
Added after 11 minutes
Race -
Swamp AbominationsStyle — Chinese architecture. Favorite magic — none.
The image is taken from Heroes 3 with some changes towards Chinese culture.
The race will be the ideological opponent of the Nagas.
Basics:
I haven't thought it through, but 2 or 3 of their units will be lizardmen. Or other creatures from Chinese mythology. But the ranged units should be lizards with Cho-Ko-Nu, an ancient Chinese crossbow that allows firing 2 times instead of one.
Elite units:
1. Zhuge Nu — long-range firework systems. Controlled by lizardmen.
2. Wyverns — from the 3rd game.
3. Huge humanoid crocodiles dressed in ancient Chinese armor and armed with poleaxes.
Expert units:
Hydras, good old Hydras.
Lore:
Also a race not made with an emphasis on Ashan's lore, but it could be done as if they emerged from the seas and settled the swampland, and then waged war on the Nagas. After a long struggle, both nations went underwater to fight there. By the time of Heroes 5, both races were occupied by the war.
Added after 14 minutes
Race -
Army of MoraStyle — a chaotic crossbreeding of architectures. Favorite magic — none.
The image is taken from Dragon Age and The Lord of the Rings.
First, the lore:
The mages of the Silver Cities conducted experiments to crossbreed elves, humans, and orcs. But at first, they failed, and then, using the blood of breeding demons, they managed to create a very repulsive hybrid, which they called Uruks. They began to multiply very quickly, which led to the Silver Cities army fighting them. They fled to the dungeons, the lowest dungeons they could reach. There they created a huge army and....
Troop composition:
Completely unknown, but the Uruks emphasize reproduction and the spread of contagion to enemies, turning them either into Uruks or into something else and incomprehensible. Uruks also use infected insects and creatures. In general, they are very similar to the Zerg from Starcraft. Their overall appearance should be repulsive.
Added after 1 minute
And in addition — the list I presented above is the list of all the races I would like to see in Heroes 6 or already in 7.