Here's my two cents:
Sedley at his finest: he discusses how the proem to book 1 is a direct response to Empedocles' poem On Nature and a transition from Empedocles philosophy to that of Epicurus. Then he constructs the contents of Epicurus' On Nature and has a couple of charts showing how this correlates to Lucretius DRN. Later he posits that the final book or two of DRN correlates to the Peripatetic Theophrastus via Epicurus.
He further posits that Lucretius was in the process of a rewrite at the time of his death, and that he had only completed books 1-3. His theory is that Lucretius first put Epicurus On Nature into verse, then was reworking the structure of his poem to fit his goal of persuasion as opposed to Epicurus' goal of exposition. He describes Epicurus' books as the contents of a series of lectures, btw.
As to the plague of Athens, Sedley's theory is that it was Lucretius' initial pass, to be reworked. He presents the overall DRN as a cycle of books beginning with pleasure and ending with pain, and posits that the plague of Athens portion would probably have been reworked to show how an Epicurean deals with pain, similar to Epicurus on his deathbed.
He's kind enough to translate 99% of the Greek and Latin; overall it reads quite well for a layman such as me.
Makes me want to read DRN yet again!