The Road to 5.0

[Fenral]

If they do got the route of introducing a new princess character, her name would have to be Sarah. There's simply no way around it. There's even wiggle-room to misspell it slightly (Sara/Sarah/Serah), as needed to best fit naming conventions.

Or perhaps it's her first shard counterpart (assuming they do such things, despite historical drift making such direct parallels ponderously implausible)?

I believe that level of historical drift is already canon, down to even languages being different between shards. (Arbert wasn't the WoD's real name, and he had the Echo to get around language issues.) I think the closest analogy is the various parallel Earths seen in the original Star Trek. There may have been some similarities in the distant past, but they would have since spiraled out to the point that nobody has a parallel-world twin or anything.