I will agree with some of the commenters above and say that I DON'T want them to just add content about Byzantium restoring the Roman empire. If someone wants that, CK2 has them covered already.
A new Byzantium should be satisfied with having conquered all of Greece, all of Anatolia, and maybe parts of Syria, Bulgaria and Serbia, as far as missions go. If the devs want to really go crazy they can give missions for the conquest/vassalization of all European territory south of the Danube and then have a mission to take the areas around Antioch and Jerusalem (including their provinces of course). That's about as far as the Post-Heraclius territorial amibitions of the empire could extend (with Basil "the Bulgar-slayer" subjugating a large portion of the Balkans and Manuel Komnenos having indirect overlordship over the Principality of Antioch and the kingdom of Jerusalem, for a brief period).
There is great opportunity, as pointed out above by
@HypnoSkales , to delve into the final religion of the empire. That is, whether the emperors successfully impose a unification of the churches under Rome or become Orthodox again due to not needing Latin aid anymore. They could lean into the cultural consequences of that (with a more Eastern and Russia-like historical development if Orthodox, and a more Western, Italian-influenced, development if Catholic) as well as the cultural shift that historically happened after the enlightenment with neo-Classicism and Philhellenism. Come to think of it, they could even add some "neo-Orthodox" path, where Byzantium goes Catholic but then joins the reformation as Protestant or Calvinist, having been cut off from its Orthodox roots for too long, though that may be too bizarre to think coherent alt-history scenarios about.
In political terms, the cultural consequences could mean the development of a English Commonwealth-esque attempt at returning to Roman classical republicanism, a bigger emphasis on the spiritual nature of the Imperial throne, leading to something like the Russian Tsardom or post-Meiji imperial Japan, or a more Roman equivalent to the British synthesis of Parliament and crown, with a senate - emperor balancing system. There could also be a more "militarist" empire, like what exists for Prussia or the Teutonic order, where it is purely the army that has legitimacy to crown emperors.
In general, one of the most interesting things about Byzantium was this idea of an emperor who, at least theoretically, was chosen by the citizens, army, senate or any combination of the three, and how that had not been codified as a succession rule up until its end, as well as the simultaneous articulation of the spiritual role of the emperor as "God's viceroy on Earth" and the theoretical ruler of the entire world. Any of these ideas could gain dominance as the codified basis of legitimacy for the country in the new age of constitutions and elaborate legal codes that late-game EU4 is trying to represent.
The Byzantine empire never actually lost its Greek identity, even when calling themselves Roman. In practice, it was Roman governance and Greek culture that existed in Byzantium since, at least, Heraclius, if not earlier. This composite identity still has echoes in modern day Greece, what the devs need to do is research that unique mix and turn it up to 11. This will be highly interesting and engaging in my view.
With Imeriti being gone in 1.36, it’s going to be harder to expand and I hope that Trebizond maybe might get its own unique missions to restore the East
.png){kind=avatar}
