I once toyed with an OTU variant called Sol Invictus. By the 1100's, moderate winds prevailed in the Solomani leadership. However, preparation for the inevitable "Round 2" of the Solomani Rim War continued with full steam ahead. In this setting, the Solomani bided their time and waited patiently - a moderate government taking the long view and reigning in the zealots helps with that - until the early-mid 1120's. By then, both major sides in the conflict demanded so many naval units and so many taxes from the Rimward sectors to fuel their unwinnable civil war that defenses on the Solomani border were spread very thin.
Then the Solomani struck with unerring precision. They had good intelligence and many years to prepare. They steamrolled over the weakened Imperial defenses. Within a month they took Terra. In seven more months, they reclaimed their old Sphere and reached the Zarushagar-Massilia-Delphi "neck", where they stabilized a frontier. They were wise enough not to stretch themselves as thin as in the old Rule of Man, and were wise enough to avoid intervening in the big Dulinor-Lucan war itself.
The year now is 1140. There was no Virus. Dulinor "won" the Rebellion in the 1130's and is Emperor. On paper, he rules 11,000 worlds. In practice, he hardly controls 110 - and most of them heavily devastated by decades of war. He bled Ilelish/Verge dry by taxation and conscription to feed his war effort, and eventually this led to an uprising, forcing his daughter to flee to Capital while his former subjects formed the Verge Combine. Around the Rum Imperium ruled by Dulinor there are parsecs upon parsecs of devastated blight, haunted by raiders and pirates. Solomani space, in comparison, is safer and more prosperous. The moderate Solomani government took a "Sol Man's Burden" view of alien affairs; for the most part, this means paternalism and coercion towards non-Solomani, but no ethnic cleansing (to the disappointment of the hardliners). Solomani forces are spread thin, however, and there is much lawlessness (and thus room for PCs to make a difference and/or engage in crime) even on the Solomani periphery. There are also local Solomani hardliners who take far more extreme stances on alien affairs than the government on Terra.
Of course, as most Solomani forces are spread in their new territories, the Aslan might be brewing something in the Dark Nebula, where only a small garrison remains...