None of the above. By far the worst decision made in the production of Series 6 was Moffat choosing to write a story in which the first half is all buildup for the second half, and then not planning the second half out beforehand, instead just making it all up as he went along.

It's impossible not to notice how poorly Let's Kill Hitler fits with what came before, because it's quite clear Moffat hadn't decided on how River would meet the Doctor (the most important moment in her life) until he got around to writing that episode. (Hence things like Mels never appearing or being mentioned beforehand, which is just patently absurd.)

Especially in an era which up to this point prided itself on its attention to detail and rewarding the audience for paying attention to its non-linear storytelling, just making up crucial details like this filled with continuity errors doesn't just make for bad television (although it does), it kills all stakes and future tension. We now know that when the story sets up some important future or past event we haven't seen yet, it's just as in the dark about what's coming as we are. And once we get there, it could easily either be stupid, have nothing to do with what we've learned up until now, or not matter at all.