If at some point the Alpha Legion gets involved in the conflict there would be a pretty simple and plausible reason to have imperial factions fighting each other: paranoia. After all, what if those other guys were being infiltrated and/or manipulated? At the 41st millennium trust, even within the Imperium, is a very fragile thing.
Clearly, Malal will have caused some sort of Warp Dickery to have all the IoM factions fight each other. Also, My solution to the Sororitas being lesser than other factions would be Acts of Faith.
I still don't see how people think an 8+ side war is ever going to work in a game. It'll fragment the community so much, it's insane. You'll never find decent battles that way.
I don't think we will ever see 8 factions... personally I think that some factions might not have a player base large enough to make it worth the money they will cost to develop... I would be glad if I'm wrong.
I love sisters of battle, but maybe they'd work better as a sub-faction to the space marines. I mean, they have a similar troop lay out, just with their own flavour. Less sturdy, more miracles. I don't really want to play the zerg faction, though. Is why I'm going Eldar.
If IG is a Faction on its own, then having all Sub-Factions as a Tank army will quickly become boring. You need Characterful Sub-Factions, and the easiest way to do that with is to have each one represent a different type of Regiment. That way you have the maximum playing options for any Faction. You can have the 'Vanilla' IG Regiment, the Heavy-Support/Tank-Heavy/Mechanised Regiment for those who want to play those roles, the Scout/Recon Regiment for Stealth and Saboteur players, and Rapid Reaction Regiment for those who want to jump from aircraft and drive fast vehicles (Stormtroopers?). But you will have to use the Veteran and Elite units from these Regiments. But it will help if they are Veteran and/or Elite Regiments. The only other way is to have the rest of the IOM armies, including IG, as Sub-Factions of an IOM Faction. Though I suppose you could start them off this way and split them off at a later date into their own Factions.
The devs have said that no subfactions in any faction will be "the tank faction" or "the assault marine faction", etc. Any bonuses they get are more in the form of very situational, often utility benefits. Every subfaction can fill all the roles within the faction, just some have a little flavourful benefit for some roles. Making an IG faction with that format is thus not possible.
Don't tell me. Tell Alchy. I was trying to tell him one reason why a Tank-Faction was a bad idea, hence my reply to him. You've just provided another reason. My characterful IG can still fit in with the information you've posted above. Just takes a bit more finagling.
I was just giving an example, and there are tons of different armour specializations. From mechanized infantry to heavy armour divisions, or scouting ones. Armour is not one-dimensional and you can subtract as much variation as you can infantry. You also forget my mention of the Imperial Navy, from bombardments up to sending drop troops. Ever Guard regiment uses armour in their own way, btw, so having each with their own specialized armour is not a bad idea to me.
