Not sure if this answers your question, but if it really bothers you, you could change the CSS rules that your browser applies to a specific site. If you are using firefox, the file to edit is `chrome/userContent.css`.

I know it doesn't help others, but in my experience people using such software actually like this retro look (and I agree it does have some appeal to it - function before form).

I think my issue is more with navigation than style. Like Seeing the whole thread tree inline would be nicer no, even for the folks who still want the plain text feel?

There was Gmane. Too bad nothing had replaced it. It was the de facto site used when sharing links to mail list posts and it did have thread navigation that made sense.