came from tiktok, however I can't play the game as I lag too much and it kicks me out so I hope the best for you but I unfortunately can't play
I do have some ideas tho from what I played:
allies
peace treaties (more options such as vassals, limit army or take reparations)
air & navy - port or airbase for extra benefits in war and blockades
select multiple units at once by dragging mouse
form new nations
encirclements
capital city
make the spectator when you enter spectator in the tab console. and to enter as a nation write the nations name in tab/ console
events - e.g. famine, union, floods, resource detection, president dies/ assassinated etc...
civil war due to party split (low chance of occurring)/ revolt from annexed states
united nations or Eu sort of thing, not a military alliance but for events, votes, economic or events
(I'm not sure because I haven't tested) the pacific should should be connected from japan to America in any way possible
(this is more extreme to do and is not necessary) Create maps for different dates such as 1444 or 1936. Could include colonization and different soldier skins for each date
Last idea I got is a tech/ political tree. This could be for extra benefits for certain nations, alliances, world wars or for the tech.
good game though, not that I have played much I hope much success from you and your game
you can choose to add none of these, it is your game in the end but make sure the game works without bugs before adding new new feature and add essential things like the selecting multiple troops at once
:)