The question then becomes, "Has the Imperium always been dominated by Homeworldism?"
If so, then the Rebellion war becomes less of a Revolution and more of a "World War" on an interstellar scale as the forces you've listed slug it out for differing and conflicting goals. For example. (note that individual's names refer less to that single individual and more towards the faction/region that individual represents)
Dulinor wants to bring the Imperium under (his) centralized control.
Lucan operates under the delusion that the Imperium is under centralized control, and wants to bring all of the factions "back in line".
Margaret understands that the Imperium was more of a vehicle for interstellar trade and commerce, and wants to wait out the hostilities so business can return to normal. I'd venture that this would be Strephon's goal as well (except that he would have the additional goal of regaining his throne).
The Vilani would want to also return to a stable, business and commerce freindly environment, but with a stronger, more culturally Vilani slant.
Antares and Diabei are a harder to pin down, but if we make them more regional with unique cultures then they would resist and be targets for Dulinor and Lucan.
Norris wants to protect the idealized and romantic notion of "Imperium".
And the neighboring powers involve themselves based on their own strategic policies, some take the opportunity to invade and add a few systems at the Imperium's expense (like the Aslan and Solomani), others watch the war from the sidelines and keep the chaos from spreading into their territory (like the Zhodani). And Pirates just take advantage of the situation to "get rich quick".
This would be very hard on the infrastructure of the Imperium, provided the Dulinor and Lucan factions remain as tenacious as they have been presented in the MT source material.
Where I would really differ with the published source material is that each of these factions is more than the single person that represents them. In other words, It's not that Dulinor shot Strephon, but that the Dulinor-led faction attempted to seize central power in the Imperium. Thus, simply eliminating/deposing/arresting the leader of the faction may not stop the faction from continuing its fight.
Strephon's family would not necessarily need to be assassinated in this model. I'd still kill them off, because for the war to become as destructive as it does, we really need someone as petty and vindictive as Lucan in charge of his faction. If there were someone reasonable calling the shots, then cooler heads prevail, and that would keep everything from collapsing. Or at least prevent the "scorched earth" policies from gutting four or five sectors.