I cannot see the dev team being capable of implementing that level of detail for the Byzantine empire to work, because the game as designed never give much thought to non-feudal gameplay mechanics. Playing as the Byzantine empire is to play a management simulator. If the team did not think about implementing those mechanics early in the development cycle of CK3, then it is far too late to ask for any meaningful Byzantine DLCs.
Same with Rota succession system.
In Eastern Europe, succession was a messy business. One of the features was that a land was never set to be owned forever by a branch of family (non-main inheriting brother for example). Instead, while key successor would become a duke of main title, rest according to succession queue would gain other titles. If you as a duke of Chernihiv became a duke of Kyiv, you would normally relieve your title of Duke of Chernihiv.
Notably, it was modified later to make patrimonial lands an exception for major duchies when Rus reached peak and, effectively, those "duchies" were sizes of Kingdom (Chernihiv, Galicia-Volhyn, Vladimir are biggest examples that span across dejure kingdom sizes).
The system survived well into XV century until it was fully scrapped, with Muscovite civil war being one of last major cases of it's manifestation (it ended right around the end of game timeframe).
The problem is that it couldn't be easily made in CK2. Court for many such princes was a separate thing from local title. In fact, to an extent even landless succeeding princes had courts and rights. If their turn was skipped, a war would break out (with a help of allies but still). When they would succeed, they would move their court to a new title.
It is a distinct modification of classic feudal gameplay that, like Byzantine, to some extent needs having landless (in classic meaning) characters as playable. Can it be done in CK3? Just like Byzantines, probably not.
I understand a desire to have separate DLCs for regions. But it seems that they are doing CK2 mistake of not supporting such systems in hardcoded way and would use workarounds of CK2 instead. It is a terrible prospect, these two unique systems (Byzantine + Rota) were those elements I wish were better in CK3.