I voted for Gaul, Maori, Norway, Phoenicia, and Vietnam. I'm particularly keen to keep Phoenicia rather than Carthage unless Carthage gets portrayed more like Phoenicia. Many on this list I want to see replaced:
Cree with a new NA civilization.
Georgia with Armenia.
Scythia with Parthia.
Hungary with Bohemia.
Scotland with Ireland.
Mapuche/Gran Colombia with Muisca.
I'd be okay with Maori and Vietnam being replaced by other Polynesian and SEA civs respectively, but I'd also be okay with their reprise. Similarly, I think Norway is a solid choice for the Viking civ, but I'm open to seeing it replaced by Iceland or Denmark--though, truth be told, if we see Denmark again I'd rather see it as post-Viking Kalmar Union Denmark, albeit that would likely come at the cost of Protestant military powerhouse Sweden.
Canada and especially Australia I just don't want to see come back.
Regarding the Parthians, yes, they were the Arsacid Persians, but if we're going to have an ancient/classical Eurasian steppe civ they really are the best candidate precisely because they eventually settled down and founded cities--no naming cities after archaeological dig sites. Khazars are interesting but are Medieval (albeit early Medieval) and thus fill a different niche, same with the Timurids or the Alans. The problem with other ancient/classical horse nomads--Cimmerians, Scythians, Kassites--is that finding leaders and city names is difficult. (I'm not suggesting we need a horse nomad civ for each age. I think Civ6 has too many of them. But Civ6 Scythia's niche is definitely the early horse nomads, in contrast to Mongolia's Medieval horse nomads. Subbing the Khazars or Timurids doesn't fill Scythia's niche.)
Also, since the legitimacy of the "unending line of Chinese history from Zhou to Qing" has been questioned, I don't think it's unfair to question the legitimacy of the unending line of Persian history from Achaemenid to Pahlavi, either. Indeed, I'd argue it's even more open to question because Persian culture was suppressed for some time after the Islamic conquest, leading eventually to a resurgence of Persian culture and a rejection of Arabicization and Turkicization. At any rate, Sid Meier's Persia is and always has been exclusively Achaemenid; the Parthians are a golden opportunity to bring in later Persian history under a different name. (That would be much harder to do with, say, the Sassanids, alas.)
That being said, replacing Scythia with Parthia doesn't mean I don't want more Central Asian civs, be it Sogdia, Kushan, Kwarazmia, Afghanistan, Timurids, Uzbeks, Khazars, whatever.