In The Bible As a Divine Witness to Human Revelation, I read Paul D. Wegner's essay, "Seams in the Book of Isaiah: Looking for Answers." According to Wegner, there are seams in the Book of Isaiah that are marked by three introductions (Isaiah 1:1; 2:1; 13:1) and three refrains (48:22; 57:21; 66:24). Wegner identifies the seams as 1:27-31; 4:2-6; 39:1-8; 48:17-22; 57:16-21; and 66:18-24.
For Wegner, the message of the seams is that "God will purge the nation of Israel and bring forth a righteous remnant, but the wicked will be punished" (page 93). Wegner continues to state that "The final refrain is more climactic, as the remnant it describes comes not only from Israel but from all nations (66:18-19)."
I'm not sure if Wegner dismisses the three-fold division of the Book of Isaiah. My impression is that he deems it to be inadequate in fully describing what is going on in Isaiah, and yet he acknowledges that the book contains different perspectives and reflects different times. For example, parts of Isaiah speak of a Davidic king who will preside over an era of peace; other parts call Cyrus the Messiah. Parts treat Assyria as the villain, and parts talk about Babylon. And yet, Wegner observes commonalities in theme and vocabulary throughout the Book of Isaiah. Wegner's argument may be that redactional hands gave the book a certain inner unity. Or perhaps Isaiah inspired a school that interpreted events according to his ideology (not completely, but in a number of areas).
One point that interested me: In Isaiah 39:8, King Hezekiah of Judah, when he hears that the Babylonians will conquer Judah after his death, happily exults that there will be peace in his days---while he is still alive. Wegner speculates that this may be a contrast to the refrain repeated in the Book of Isaiah: there will be no peace for the wicked. Hezekiah, however, was righteous, and so he experienced peace.
I wonder if that is going on in the Book of Isaiah. Hezekiah says that there will be peace in his days in II Kings 20:19, so, when Isaiah includes that line, I wonder if one of the authors or redactors of Isaiah is making a big deal about Hezekiah's statement, or if he is simply copying the standard version of the story---like a copy-and-paste sort of deal. But I was interested in Wegner's take on Hezekiah's statement because I too have wondered about its significance: why does the story mention that detail? For me, Hezekiah sounds pretty selfish---like he's saying, "Who cares what happens to the next generation, just so long as I am safe?" But what does the storyteller want us to conclude from Hezekiah's line?