RE: Issue 1: Font-weight and headings
For me, the key issue here is the intention of the author. If the author of the document requests that a portion of the text be "different in some way" than the other text in the same container, then the UA should do its best to accommodate that intent. In this example, if there is any way to make the enclosed text "bolder" than whatever the Hn is styled for, then the UA should render accordingly.
[aside] I'm glad that I'm not a UA author! What a job, eh? [/aside]