Let’s discuss the Brotherhood Expansion for Siege of the Citadel.
Not much is know at this time of writing what the expansion will include in terms of new rules. We know it will contain the Brotherhood faction, new creatures and cards.
Probably, we will get rules about the Art of the Brotherhood. In the old game, these were new Doomtrooper cards that were specific to the Brotherhood faction. There were three cards, each with two different spells to choose from.
There was also a few new rules with the old Sinkadus expansion. AIMING is kind of replaced by the new Concentrated Fire rule and AUTOMATIC FIRE is probably better instanced in certain weapons as of now. But I think PUSH is really cool, I wonder if it is in the new expansion rules somewhere?
From old Sinkadus Brotherhood expansion:
AUTOMATIC FIRE
By spending two actions the miniature may fire a long, forceful burst that allows him to do an attack against all miniatures in his line-of-sight. The miniatures have their armour raised by 1. Very effective in a corridor filled with legionaries. Automatic Fire may be done by all weapons except the Genehena-Puker and the Grenade Launcher. The miniature may decide when he wishes to interrupt this action, since there is risk to hit one of his own.
AIMING
By spending two actions the miniature may aim extra carefully and fire a very well-aimed shot. Roll one extra dice and re-roll one dice of your choice. You may not aim with the Gehena-Puker or the Grenade Launcher. You may also not aim if you start your turn next to an enemy miniature.
PUSH
Sometimes it’s easier to push (if you prefer, tear) away another miniature than to kill it, especially if you only wish to get past it. Very useful in a situation where a competing Doomtrooper blocks your path.
A push is executed as a traditional melee attack, but the pushed miniature also rolls his attack dice. If the pushed miniature rolls less hits than the pushing one, the miniature is moved to an adjacent square of his choice.
If the pushed miniature rolls more hits than the pushing one, nothing happens, but if the pushed miniature rolls double the amount of hits than his pusher, the pusher moves one step backwards. You may not push more than one miniature at a time.
The Brotherhood expansion has my favorite Dark Legion miniatures from the kickstarter and they all received special abilities for SotC, so I can’t wait to try them out.
The Brotherhood expansion has my favorite faction 
The Push rules are not in there, but could easily be house ruled. But there is a difference between the new Siege and the old Siege in that you can now pass through any Doomtrooper now (for those belonging to another player you need their permission). This kind of makes Push obsolete, at least for other Doomtroopers. Might be usable against DL creatures though.