Yes, topic summaries would be an excellent way for new readers to get up-to-speed. Plus, with an ability to view a wiki-like revision diff of a summary since your last visit, a quick way to catch up.
As you’ve written, summaries should include permalinks to individual replies, so that people can read the sources of the aspects of the summary that interest them.
Two suggestions:
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A summary should be associated with a list of the replies it summarises. This makes it easy for those writing summaries to filter replies by their currently unsummarised (and unedited) status, and so easily incrementally summarise replies from only this pool, including new replies as added.
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Instead of a single summary at the top, allow multiple summaries, which can each be normal replies that have a summary tag. Multiple summaries are useful when there’s more than one side of a contentious argument (preventing edit-wars on a single summary), or when there can be sub-topics (in which case replies to a sub-topic summary can form the root of that sub-topic’s second-level thread).