Some excerpts from Treasures of Ashkenaz, here:
I want to re-analyze what is מנהג ארץ ישראל. I am living in Eretz Yisroel over fifty years, I don’t know yet what is מנהג ארץ ישראל.
He goes on to describe a street in Bnei Brak. “… there are אפשר seven apartment houses of twelve apartments each and fifteen shuls. And each Shul is different. This is a Bukharan shul, this is a Yemenite, this is Sfardi,…this is the Kuzhmirer, this is the Spinker, and everything…” ……. two brands of Spinka…. now we’ve got three Vizhnitz in Bnei Brak….This is (a singular and unitary) מנהג ארץ ישראל?
He goes on to talk about מנהג ירושלים :
מנהג ירושלים, this is considered to be the epitome of מנהג ארץ ישראל. Rav Shlomo Zalman (Auerbach זצ”ל) told (a relation of his) that I have a kabboloh, from Rav Dovid Baharan, Rav Dovid Baharan was a poseik in Yerusholayim, az ‘oib einer vet kumen tzu eich un vet zogen dos iz minhag Yerusholayim, zolst vissen, er iz a ligener, veilst s’iz nisht doh kein מנהג ירושלים’ (there is no single [unitary] minhag Yerusholayim).
…
Note: The Chazon Ish makes some interesting points in this manner in CI Yoreh Deah 150.