I think nearly every world in the core sectors should be under direct Imperial rule, as is hinted at in the early material, and that they have been economically developed into cash cows for the nobility. I was never a fan of just extending Spinward Marches randomness to the whole Imperium.
I rather like the idea suggested in T4 for Milieu:0 that the basic concept of the "Rule between the Stars" was part of Cleon's concept from the beginning in the Core in order to generate "buy-in" to the system, with the Imperium regulating trade and dealing with piracy and rogue states and taking its cut in return as part of the deal thru the Nobiliary system, sweetening the pot with access to FusionPlus.
But of course, the real plan being to over time insinuate themselves into positions of local power thru intrigues and intermarriage and dominate the trade system thru undercutting and buy-outs, and choking the trade of non-complying entities, and eventually becoming effective overlords thru proxies in the "local" governments, or through individuals outrightly wearing multiple hats in both local and Imperial offices of nobility.
And then came Artemsus and the Lentuli Dynasty, the military expansionists . . . And the subsequent unsettled period of the non-Dynastic Emperors . . .
So with the various wars and revolts (Ilelish Revolt, Julian War, Civil War, Rim War, other Pacification conflicts, etc. ) I can see somewhat of a bit of both of the "direct rule" on some worlds, but shrewdly relaxed in many places in the 11th Century in favor of a more Cleonian/Kerrian-vision "local government" that toes the line before Imperial Overlords and their interests in the Core.
But I definitely like the idea of preserving as much as possible the "Frontier Feel" of the Marches and Backwaters, even if they have been settled for some time, even if that takes some tweaking.
But that is my take.