To sum up, the last episodes are supposedly funny, deal with Jimmy trying to find some kind of resolution within himself, are way different from the structure of the rest of the show and even any other show in general, and the cast/crew seem very excited by the story being told in them.

Carol Burnett will guest star, and I am pretty sure David Cross will be featured as well based on Bob's response of "Which one?" when questioned about a cast member of Mr. Show (which was John Ennis) being featured in 6x07, followed by him realizing he slipped a little. I was under the impression he caught himself because another Mr. Show costar will arrive towards the end.

Could the end of the series take a cue from the American Greed promo and deal with an in-universe movie/show/production based on the Walter White/Saul Goodman saga being created? Jimmy being consulted about key moments from both shows, forcing him to re-contextualize certain moments from his life and see them in a new way after years of introspection?

It fits thematically with the series as Saul was always something of a film director. It also gets to the heart of the show's focus on identity as a self fulfilling prophecy and something you choose to project to the world. What better way for Jimmy to TRULY grapple with "who he really is" then to see himself as a character being created for a real audience to absorb. Its super meta and connects big ideas of the show in terms of the performative self vs. the true self.

They could cut between parts of the "show within a show" being shot, and contrast it with the actual events (i.e. key moments from Breaking Bad) to highlight how certain moments can be reframed/embellished and take on a new life in retrospect. Carol could be any number of people, Jimmy's mom? Irene?

Its an idea that sounds too crazy and jarring at first, but the more I think about it, it is perfect. Consider the ongoing student film crew characters trying to make it in the film industry, Jimmy and Kim's love of watching old movies together, the first scene of the series being Gene glumly re-watching past highlights of his life on a screen with rose tinted glasses. It just fits.

It could also set up a perfect last shot of the series to tie back to the opening scene. Gene sadly looks at his old Saul commercials with a drink in hand, clearly feeling regretful and melancholy. Contrast that with an older Jimmy sitting in the audience watching this "movie" about his life in a similarly framed shot, except we are in color instead of black and white, and he doesn't look as completely broken as he did in that pilot. He looks slightly amused, slightly embarrassed, slightly proud, of the totality of his life being presented before him. He has finally accepted who he is and he is done hiding.