obviously if there were scouts, heretics and snotlings, you wouldn't want your entire team to be playing as them. scouts are obviously a niche, and heretics and snotlings are clearly weak. they'd all die without bleedout, and have no armour.

so to avoid "RTS guardsmen" talk, why not add them as elites? that way a couple of the team could be scouts, getting a few lives and covert equipment, like the stalker bolter and shotguns, but also explosives, and obviously a cloak.

or a few people could be annoying, speedy little snotlings, whose role would be to be speedy and annoying cannonfodder. snotlings wouldn't do much DPS but perhaps they could be animated to clamber onto enemies and beat them up until pulled off, and maybe they could use veteran nobs as vehicles. (IE jumping onto a stormboy nob so he can fly you and your snotling pals to victory)

heretics would get bonuses for their god, tzeench giving invisibility, or perhaps the power to change appearance (a bit like TF2 spy), khorne making them into a bomb, nurgle giving them armour and bursting poison on death, and slaanesh giving psychotropic drugs that make the enemy think they're being attacked when they aren't for a while (spawns fake, ghostly chaos space marines nearby that start attacking, but do no damage)

guardsmen could also be added under the same idea, but they're AOE recievers. they have 34 armour when standing close to space marines.

eldar get NOTHING

We all want similar sort of stuff, but it is going to require a lot of work the development team can not support.

They can't make Gatekeeper's Bastion moddable for like ages. (Facing the fact that they started working on it like 2 month ago) and you expect those people to make new textures with new animations and etc? Like even orks keep looking like race of small land-walking krakens...