I think in reality she makes the most sense for a number of reasons
1. She knows everyone (bar Lilly) from season 1 and as Clem has been confirmed, I just think it wouldn't work that we know clem but the new protagonist doesn't
2. She cares about clem, Not as much as Lee but still a lot and likes Omid which most fans also do.
3. She's kind of ignored by fans, she isn't loved like Clem or Omid and isn't hated like Lilly or Kenny (I'm not saying everyone feels like this just an example) so people wouldn't mind playing as her and be effected by pre - existing feelings.
4. She doesn't have special abilities like Vernons medical skills or Molly's ninja abilities (protagonists in this world need to be normal people without any special skills)
5. Her personality would make sense in most situations. Omid/Clem letting people die or Kenny saving a bunch of strangers wouldn't make sense but Christa could do both and it would stay true to the character.
Of course she is pregnant (probably) and there are other issues too I just feel she fits the bill most for a new protagonist.
So does anyone agree that she would make a good protagonist?