Just so it's on record: State of Hatay in Syria which was historically given to Turkey in 1939.

More City States?
As In London and the Greater London Area etc..

Split Baden and Württemberg

you can add nice and upper savoy for italy, the lybian desert that italy had in 1919, then also the fiume city, ioanian islands, suez canal, albania split in two, costanta province for bulgaria, some coastial cities in china, burma's provinces reworked, kashmir state reworked, central asian provinces reworked better, caucasian new nations like mountain republic, cechnya, dagestan, abkazia, ossetia, don kuban union state. there are also mongolian provinces, french rhine border in germany and netherland, swiss cantons like schweiz, suisse, ticino.

There are a lot of ideas more... if you want.

you could add a bunch of states from the kaiserreich mod

French Catalonia

WEST VIRGINIAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

rosellón

Maybe split east prussia in a eastern, western and southern part as states.

Also i'd like a split luxembourg.

You could split south tyrol into trentino (southern half) and südtirol (northern half), thus fixing the mess with the italian/austrian cores

Hatay and splitten tyrol is done.

Splitten luxemburg is impossible

They should add in the microstates and Kosovo.

Maybe make borders for the Kingdom of Bohemia possible?