These etiquette issues take care of themselves, to some extent. A while back, when smartphones "happened", there were loads of people using them to broadcast music on public transport. Eventually, these people have the experience of being on the receiving end, realise how annoying it is, and a new social norm develops against doing it.

I think there are two areas at the moment (like OP pointed out) where the etiquette hasn't formed yet, because the tech is new:
* Children with tablets (they only recently became cheap enough)
* Video conferencing on the move

My hunch is that in a few years we'll see this take care of itself. The people who are on the receiving end of kids with tablets will think differently when they have kids themselves, and be more considerate. Facetiming will become so common that people aren't so wrapped up in the novelty, and will start to be more discreet.

It's optimistic of me though... I would have hoped a social norm against bringing your mcdonalds onto the plane would have formed by now but I'm still waiting!