'toss in Starcraft are not just psionic, they are also very technology/ai based. think reaver and carrier.
it would be very kewl to have an alien weapon with robot projectiles that could be controlled psychically and had a slow recharge rate like the dragoon barb, but could be steered along the ground and exploded on impact. the downside would be that the user was totally immobile while doing this, and the projectiles would move slowly and would be die harmlessly if you shot them.
i think since humans have long range and ok movement, while aliens have short range and awesome movement, give the new aliens low hitpoints and average mobility, but with stealth, high damage, and AI technology.
they could have a walker that is like a cross between the battlesuit and dragoon - heavily armored, moves in one direction quickly, but not that maneuvarable in tight quarters. also could have unlimited ammo but a slow fire rate.
it would be interesting trying to find a balance there. i have always thought it would be loads of fun to play SC in first person.