Lots of thoughts...not sure what would be the best solution for you.
I'm assuming your goal is to put the content or a link to the content on the users "My Space" or do you want to email the content out? or both?
Using News might be an easy and appropriate fix. You could add a link to forums [post this message as News] and have it automatically insert the message text, or the first N characters of the message with a link back to the forum thread. A nice feature of the News module is it will automatically expire the messages on the date you specify. Each community has a news package and they are all aggregated to the user's "My Space". Sloan uses an "All Sloan" group that they use to give them a "site wide" feature.
I can think of some cooler but more involved solutions also. But first some questions.
1. How much content do you want to display? Just a title and a link or a significant amount of text?
2. Do you just want it site-wide or do you want to highlight info by community.
3. Who will be able to designated which content should be highlighted? A site-wide admin? A group admin? All users?