Threaded Comments Should Use Heading Levels to Communicate Reply Depth

@terrill pointed out in #1272870-92: No semantics for nested comments / bad for screen-readers → that threaded comments could be used to track the depth of the reply.

I was thinking about this too and think that there are some real strengths to this idea.

Couple things to consider:

• You'd want the semantics to change but not the size. This could be accomplished with CSS, but it would be a tricky pattern.
• If you allowed headings within the body of the comments, where would you start? Allowing anyone to insert a H4 would be fine until you're 2 replies deep at which point it starts to break the semantics.
• What happens if you're 5 replies deep? There are only 6 heading levels, right?

Still it's an interesting idea and there may be some way to make this work.