Something that just occurred to me is that, in line with how the Sigmar-perium is kinda just the hundred different sectors of Segmentum Sol and change as a more sustainable and gradual and tied together series of sub-states and fantasy Empire provinces and free cities in space, the higher government of the Imperium outside of the Imperial court of Emperor Ioannes Schmidt IX is probably gonna be really interesting. The Empire only has 15-ish Elector-Counts and such, nominally in line with having the non-traitor titles of Legion Primarchs and more broadly just having much the same High Lords as also the viziers and council of state around the Emperor, buuuut, in bumping that up to proper space opera monumental size and grandeur for the Imperium means I think pulling some Dune Landsraad and CHAOM stuff.
The thousand envoys of the ten thousand lords of the half million-ish worlds of the Imperium Solar; a Rogue Trader and a Navigator Scion talking shop with a Merchant Potentate as a Chirurgeon-General nervously jostled the elbow of a Matriarch of the Selenar as they debated a Warrior Lodge Grandmaster all as a Knight Seneschal snuck into the chambers before the Lord Chancellor finished calling them up on the rolls. High Lords still show up from time to time as grand statesmen monopolizing offices and networks of power, I think, just that they also have to occasionally whip up further acclamations and such from the high command and the corps of all imperial general officers behind them, to stay Lord Commander Militant and thrice-selected Warmaster, and so on and so on. To do bad pseudolatin and Gothic-ify it and steal from some of the RL history of the Holy Roman Empire call it the Comitium Imperialis, the legal and quasi-legal heirs of Sigmar's Ten Thousand Companions, assembled in spiritual synods or judicial conclaves or most often in the Perpetual Diet of Terra (the one filled with the thousand thousand pilgrim-lordlings and patrician adepts of the Throneworld that often speak over the more provincial interests of more distant stars).
Actually hell, you further complicate things by setting out separate benches and chambers all House of Lords and Magnium Concilium-y and as also somewhat sub-legislatures and deliberative bodies in of themselves, the like Lords Spiritual of the Comitium as a select convocation of the Synod of Luminaries(?) on Ophelia VII, the collective leadership body of all such hero-cults and templar-brotherhoods and sectarian churches granted the Writ Illuminat by the Confederation of Light as Chaos-free and sanctified faiths. This also lets in Votann Prospect Fleets or like Ratling Undermoots or just like the Worshipful Company of Goxhandlers and Victualers and etc... come into the Diet's deliberations with some of the more bribable Lords of the Imperium as their proxies.
thoughts?