There are services like http://smmry.com/about http://smmry.com/about which offer an API. Some sub-reddits I frequent already have bots that auto invoke this AP

There are services like http://smmry.com/about http://smmry.com/about which offer an API. Some sub-reddits I frequent already have bots that auto invoke this API and post the TLDR as a comment on every original post, and it seems to work acceptably well.