I like the idea. Some thoughts;

I think you'll need a threshold of when a HN post is worthy of a summary (e.g. number of points), and a way of tracking work like a backlog of posts that are awaiting a summary to ensure you don't have duplicated work and to keep track of work volume.

Once a summary is posted, any comment afterwards won't be included in the summary. You'll need to decide if a summary of comments is written a longer time after the the summary of the post is written to get a good sample of the comments.

A summary will need to be completed soon before the peak of popularity to ensure maximum exposure and effect.