Thanks for the update! Some questions:
Are you going to model sub-national and interpersonal politics? If not, how do you intend to represent the dynamics that drove conflicts during the late medieval period? EU4 already struggled to represent non-state actors and non-unitary states -- see France flipping multiple times between unitary state and vassal swarm over the past decade.
Brett Devereaux wrote a long series of posts on EU4. Do you plan to incorporate any of his suggestions into EU5, particularly on institutions and why Europe invested in cannon while India and China did not?
https://acoup.blog/2021/05/28/collections-teaching-paradox-europa-universalis-iv-part-iv-why-europe/
How will you avoid making every country super-generic, and destroying replayability, as happened in Imperator, CK3, and Vic 3?
All of the titles released by PDX since Stellaris require multi-year reworks following release. Stellaris and Imperator today both are basically unrecognizable from their release versions. Vic3 seems to be on the same path of getting major reworks to its core systems, albeit at a much slower pace. Do you see this need for major system reworks post-release as a problem?