What might Season 3 have been about?
There are potentially infinite possibilities of what could happen to The OA, though, say, if another network were to save the series and pick it up -- which isn't totally unheard of in the streaming era. The conclusion of the series after just two chapters definitely came as a shock to the showrunners, who were looking forward to moving into production of Season 3, so we could see Marling and Batmanglij being on board with that plan. It does seem unlikely, given the show's experimental nature, but were it to happen, here's where Season 3 might go:
Season 2 entered the multiverse, and boy, are we in it! As much guessing as devoted fans did regarding the direction of the second season, few could have predicted exactly where it went. So, that being said, it’s hard to say where it would go for a Season 3.
Prairie would inevitably continue trying to put a stop to evil Dr. Hap, while also traveling with him and Homer, as she learned the three of them are a "cosmic family." Thus far, all three of the dimensions we've visited, including the meta-Brit-Marling-the-actress dimension, prove to be connected or alluded to in some capacity, so it's possible these will be the places of significance they frequently return to.
Aside from that, we can assume it would be even more unfathomable than the previous installments, as Ben-Adir said to RadioTimes, "I know where it’s going in the next season, which is NUTS! Like, unimaginable! Genuinely! Like, not even in a way I’m trying to sell it -- It’s crazy! … You think it goes there, but then it goes [starts pointing frantically] there and there and then there!"
We are ready to perform the movements so hopefully in this dimension we can actually go there!