I was thunderstruck by the ending as well, but after attempting to jot down my feelings several times, decided to take a step back and just let the thing sink in. Now I think that I should have seen it coming. Of course Ron would double down on the bewildering ending of LeChuck's Revenge. There was no other way.
And it's more complex than I thought at first. We're not switching from the reality of the Monkey Island stories back to the frame story. We're switching to kind of an interlude reality, with which Guybrush trolls his son in the same way that Ron trolled us all those years ago. Boybrush becomes the fans, the fans become Boybrush; and Ron becomes Guybrush just like Guybrush becomes Ron. All too fittingly, Guybrush-Ron would hastily concoct an alternative one sentence ending after Guybrush/the fans tell him what they would have liked to see. But that is of course no kind of "satisfying" ending within the self contained reality of the Monkey Island series.
Like many others, when I hear fans lamenting how the ending of Return destroyed the Monkey Island series, I have to think of the same criticism voiced about LeChuck's Revenge. It's actually true: The Monkey Island series was destroyed back in 1991. The hole that Ron tore into the fabric of his creation's reality could not possibly be closed. LeChuck's Revenge made a sequel impossible, and more than that, even undesirable.
... ... it's still the best game of the series and has spawned no less than four sequels. π
Maybe it's not so much the ending of Monkey Island 2 that Ron wanted to recreate, maybe it's what happened to the series after that final and all breaking ending. A new tree arising from salted earth. The new steward of the Monkey Island series will have to honor the series' spirit yet they will be utterly forced to completely ignore the authoritative ending of Monkey Island 6, the final word of its original creator. What a delicious irony.
Whoever takes up the baton to conduct these characters in the future, I'll definitely be in the audience. The monkeys are listening.