I don't think it ever will, as certain RK's invalidate other countries resistance mechanics. Netherlands for example has a whole tree devoted to taking back the netherlands from its colony in Indonesia and has various decisions causing sabotage and building resistance in its core lands as an RK these do nothing Same with a potential RK Moscow removing all potential use of the propaganda in USSR. So I think its a case of ok for the player but not ok for the AI to use against the player for the sake of gameplay over realism.
Yeah but that was exactly the idea behind the RKs, to alleviate the garrisoning from the main government and make it easier to handle.
There is also a RK for the Netherlands present in game, btw, so that argument is invalid anyway.
What we are lacking from official RKs are: Generalgouvernment Polen (can be released with that name over compliance), Reichsprotektorat Böhmen-Mähren (Bohemia and Moravia, Reichskommissariat Kaukasien (Pretty much the entire Don-area down to the Caucasian states) and Reichskommissariat Moskowien (the remaining Russia to the Ural).
While Kaukasian was never proclaimed officially, they already had preparation works for it done, dividing everything into districts, chose the leader, etc.
Moskowien on the other hand only had a designated leader but not much more officially put into it.
I would love to see a small, shared focus tree for the RKs though, which focuses on reducing the resistance (against compliance gain) among the population and exploiting the land for the Reich (giving factories and ressource rights to the Reich, increasing ressource efficiency thanks to forced labor, etc.) with strong stability debuffs in return to show the instability. Or maybe the RKs could choose to work for the Reich with said concept, or to work for themselves, reducing resistance, increasing compliance and autonomy and trying to become independent (which would only result in a war against their overlord).
I wish I knew how to make focus trees, cause then I'd definitely try to do that myself until it gets recognized.