Okay here is where I'm at, and I'd really like to hear from the folks who use this if there is anyone using this feature.
Intro-foo posts can not have a permalink page, which explains why they couldn't have a "read more" actually work. This seems due primarily to how MainList gets created, so I started tinkering in that neighborhood. What I've done so far is to create a new $disp type: 'intro', then create a new page to display this type: intro.main.php. So far so good, but I'm getting the Blog's title instead of the Item's title in the page head section.
This way the only thing affected is the ability to display an intro-type post as a stand-alone item. Which means you can do "intro main" and always expect it on top of any multipost page without other filters, AND allow for comments or (for my purposes) a very long intro item. My goal was 2 paragraphs displayed in multipost mode and the full monty on it's own permalink. I'm close, but I gotta get the title done then see how it affects the SEO settings we have in there.