I would just like to see some basic province weirdness fixed first, actually.
1. Fix the river Garonne river so that you can cross between Rousillon and Gascogne without crossing a river. It makes the region very hard to defend for France against Spain, which it never really was in history.
2. Add at least one, maybe two more provinces to Portugal
3. Add a province behind Tunisia so that someone can hold the province and it is still possible to travel behind it (like Fez does for Tangiers).
4. Make Venice an actual island province and turn its current province into a land province.
5. Turn Sjaelland into two islands
6. Create some Baltic island provinces from those attached to Finland and Estland.
7. Hormouz and Goa need to be offshore islands
8. Fix Sea Zone weirdness around Curacao, Bay of Biscay, Cretan Sea, and Ionian Sea (corfu sea zone, not Aegean Sea)
9. Make it so that it takes longer to sail to Canada than to Caribbean (rather than the opposite right now). Since we cannot model wind patterns, then we should create more/less sea zones to represent longer/shorter travel times.
10. Create islands along the Dalmatian coast that can be defended by naval power to represent Venetian possessions.
11. Stretch Navarra to block connection between Bearn and Cantabria.
12. Divide Beleares into Majorca and Minorca
13. Combined Gulf of Turku and Gulf of Bothnia into one sea zone.
14. Divide Weilkopolska, Carpathia, Santal, Jutland, Dagestan, Tripoli, Kabylia, Hormouz, Mekran, Madurai, Crimea, and Zeeland into 2 provinces.
15. Remove Permanent Terra Incognita that is historically inaccurate; between Kazan and Ural River, Mongolia, Central Asia above India, Northern Australia (around modern Perth), etc.
16. Ideally: Remove all PTI
EDIT:
17. Divide up the Bahamas into multiple smaller islands.