We shut off Main back in February to force everything into Discussion, and I still think the Main/Discussion split should be replaced (by better use of the tagging system, or by different subreddits based more about the style of interaction that people are looking for than the content, or so on), but (as mentioned then) we're going to be using Main for posts we want to make sure get into the RSS feed.
This is awkward because everything else is in Discussion, and Main is still a weird visibility zone, where stuff in Main that isn't Promoted is sort of in limbo. There are ways to improve this long-term, but in the short term, it looks like there are some easy options:
1. Open Thread comments linking to new promoted Main posts
2. Linkposts that point to new promoted Main posts
3. Something else?
(As said before, this should hopefully be a temporary measure; if we add promoted posts in Discussion to the site RSS (github issue), then those posts will show up in Discussion and in the RSS and everything is great.)