Caldeum is the ultimate solution to the levels rework. It helps connect a lot of places which would be otherwise very hard to allocate, but the best part is that there is no random factor here, these quests actually belong here. This is the main mage/vizjerei city in diablo and also one of the biggest cities in sanctuary. Like half of the median ubers belong here in act 3. On top of this, a new town is something new in median, this is as close as we'll ever get to a new act.
Once levels rework is finished (hopefully this week), I might post a worldmap overview, with all stages.
Keeping
sanctuary map in mind, this is the main structure:
Act1 : West Khanduras. Monastery and Westmarch (dunc is here) being the main locations.
Act 2 : East Khanduras & Islands (Twin Seas)
Act 3 : Entire Kehjistan: Kurast, Viz-Jun, Caldeum, Torajan Jungles, Ureh
Act 4 : Hell: Realm of Terror (all act 4 except town), Realm of Lies, Realm of Sin, Black Abyss (The Void), Black Road
Act 5 : Dreadlands / Arreat - after you kill Baal, Mt. Arreat becomes a crater, so not much lore takes place here. ForeverAlone. However, this act will include uberquests which do not fit in the game's timeline, currently via crossroads of time caves; but eventually nephalem-related (uldyssian) events will take place here as well.
Act three being a whole continent on its own; as you can see, a second town was much needed.