EP has the most zones left, DC has a good chunk but AD has none if you don't count that tiny sliver of Elsweyr between North and South (we will probably never see that either, too small for any DLC which sucks)
also Sheogorad (north of Vvardenfell)even...inside them!
Many uncharted mountains in Valenwood and Summerset, uncharted hills and coasts in Rivenspire, and so on!
Last but not least, the instances.
Dungeon-type places are already "out" the open-world map while beeing on Tamriel (Scalecaller in winter version of mountains in Stormhaven for instance).
True, one day we should go to Pyandonea (and Maormer getting playable race) ...unless ESO would die before.-Daedric Realms, each Prince has its own realm. Deffo chapter worthy, we can only go freely there and back from coldharbour atm. So 15 realms left, plus loads of others as well.
-Other parts of Nirn, islands, seaelfs spring to mind. Or other continents but do think those will be full blown expansions not chapters.
Loads of places to go.
We will never have PvE Falkreath and PvE Bravil. Falkreath is a dungeon and Bravil is too close to the PvP area.