Did He already return to Tziyon?
Malbim: I intend to return to Tziyon. My Shechinah will be fixed there like from before. Also, I will dwell in Yerushalayim amidst the nation, and Nevu'ah and Kedushah will return to them, and all the coveted things that used to be there from days of old. This is on condition that it be called Ir ha'Emes (refer to 8:3:2:2).
Why is it called "Ir ha'Emes"?
Radak: This is like He promised "She'eris Yisrael Lo Ya'asu Avlah v'Lo Yedabru Chazav" (Tzefanyah 3:13). The same applies to all of Eretz Yisrael; it mentions Yerushalayim because it is the capitol, and due to Har Hashem, Har ha'Kodesh; foreigners will not profane it any more.
Malbim: This is if they judge Emes Bein Adam l'Chavero, and they speak Emes with Emunah.
What do we learn from "Har Hashem Tzevakos Har ha'Kodesh"?
Malbim: It will be called Har ha'Kodesh if its Kohanim will be Kodesh to their G-d. I brought above from Mahari that Yisrael feared lest they be exiled again for seven reasons (refer to 7:3:3:2). Here He comes to remove these concerns, one at a time. The first was that they saw that the Shechinah did not return to Bayis Sheni. Here it says that the Shechinah can return, if they will improve their deeds, to do Emes and go in Kodesh.