Not exactly a meta, just a list of facts/hints that may suggest that the baby is actually David’s and not John’s. Also I’m relying on my memory, here, so forgive me or let me know if some of the mentioned events have incorrect sequences.
Sherlock sees David as a potential threat: let’s start from the obvious, I think. Who is David? What is his purpose in the show? He is literally thrown into the frame from out of nowhere, and he is immediately greeted with mistrust from the protagonist, which is, if you ask me, is never a good thing.
Sherlock:I think from now on we’ll downgrade you to casual acquaintance, no more than three planned social encounters a year and always in John’s presence. I have your contact details I will be be monitoring.
David: They were right about you. You’re a bloody psychopath.
So basically what I think is that we’re meant to pay more attention to Sherlock confronting David, who also turned out to be Mary’s ex for two years. My initial reaction to this was that it was simply the writers, trying to show just how ‘involved’ Sherlock was in John and Mary’s wedding. But then, the bridesmaids in lilac and the napkin folding and the case neglecting things came, and I realised that they’ve already tried to reflect that in other scenes. But let’s leave David alone for now, shall we?
Mary being too enthusiastic about pushing John and Sherlock together: I admit I’ve never, not once, found this scenario unusual or weird, and didn’t associate it with anything, that could’ve suggested a cheating Mary
(let’s also not go further about the creepy picture above, im saving you from feeling too uncomfortable)
but then hlv aired, and it struck me that there was something odd in Mary’s attitude( i mean, before turning out to be an ex-assassin and shooting Sherlock, obviously). I notices a few seemingly little, but nonetheless important changes. Here’s what I’m talking about: