[mulmen]

ON should be on another line because it gives context to bo.author_id = au.id.

[hobs]

You never write NOT ON, so no, I'd disagree that its required for all the inequalities you express.

[mulmen]

Huh?

ON is required by the syntax. Why start every line with a keyword that describes the line except the ON portion of a JOIN? It's inconsistent and has no clear benefit.