Re Tom Miller maybe having killed Danny. Yes it would be a satisfying twist and I wasn't happy with the Joe Miller ending...
BUT I am now binge rewatching S1 to sate Hardy/Miller cravings, and Tom is really such a little, little boy in that, not the slightly objectionable teenager we have come to know in S3. And the pathologist makes a big point of telling the police that Danny was strangled by somebody with big hands, which seems to basically rule out that theory.
Also I am watching Joe in those early scenes and thinking yeah, fair play with hindsight he IS being weird, you can see it from the start. Weirdly cavalier about the death of this boy and trying to minimise it and insist to everyone it's going to be ok, which at the time one passes of as him trying to reassure his wife and son, but it's not, he's trying to tell everyone and himself that what he did was not so bad.
I think now that if they're staying true to how they wrote S1, they won't revisit Danny's death, or not in that way.