You can already sort of do that… either:
- edit the first post to include the summary
- edit the second post to be a summary
Or, eventually:
- add another post and then manually. as staff, change the date on it so it sorts under the first post (not currently possible, but I think it should be)
The problem is that writing a real summary is real work by real human beings and is very unlikely to get done unless the human being or the topic is exceptional.
Having a machine summarize the topic by writing is basically impossible…