I would definitely read that Caliban fanfic/book you outline! Caliban, grown intelligent and able to trick people. And then I imagine that would be a springboard into the next stage in Caliban's development, that just because he can outsmart mainland people will not make him any more content than revenge did Prospero.

I'll be wise hereafter
And seek for grace. What a thrice-double ass
Was I, to take this drunkard for a god
And worship this dull fool!

I wonder what, or whom, Caliban is intending to seek grace from? Setebos? Prospero's god? The island itself? What meaning does he see in seeking grace, which is a fairly abstract and complicated theological topic? Is he only asking forgiveness for the past things he's done, such as attacking Miranda and planning to kill Prospero Jael-and-Sisera-style? Can he remake the island into a paradise, now he's older and wiser and the sole king of it?

Here is some poetry (http://rpo.library.utoronto.ca/poems/caliban-upon-setebos). I'm not going to pretend to have any taste whatsoever, but I like this bit about Caliban developing his own personal mythology:

'Thinketh He made it, with the sun to match,
But not the stars; the stars came otherwise;
Only made clouds, winds, meteors, such as that:
Also this isle, what lives and grows thereon,
And snaky sea which rounds and ends the same.

My personal favourite is Prospero's speech, which to me will always be the Magician's Archetype:

I have bedimm'd
The noontide sun, call'd forth the mutinous winds,
And 'twixt the green sea and the azured vault
Set roaring war: to the dread rattling thunder
Have I given fire and rifted Jove's stout oak
With his own bolt; the strong-based promontory
Have I made shake and by the spurs pluck'd up
The pine and cedar: graves at my command
Have waked their sleepers, oped, and let 'em forth
By my so potent art.