Reading the beta6 release notes gave me an idea for how to solve this. (Discourse 2.0.0.beta6 Release Notes)
They say there are now hidden tags and a webhook for tags. Combined that would allow for the explicit tagging of a post to be displayed on the site, rather than relying on the current implicit method, which will never allow for full control over which comments get displayed, and also prevents moderators from engaging in the community in a natural way, since they have to be very careful what they “like.”
(edited to add:) Hmmm, or not. Looks like tags can only be applied to whole topics, not individual posts within those topics. Is that right?
And now that I look at it, it appears that badges only apply to users, but the particular post that caused the badge to be awarded is somehow associated. My badge idea could still work, as long as you can apply the same badge to a user multiple times. Regardless, the solution to this problem requires something that can be set on a per post basis.
The only other thing I see (besides flags) that meets the bill is the “add staff color.” That probably makes more sense as a selection method, since it can be set on any post and it has the added benefit of giving visual indication in Discourse of the fact that it is highlighted on the site as well.