Within the context of Kubla Khan as a monumental testament to Coleridge's "almost-there!" failure as a conduit for inspiration, his presentation of the terrified viewing public lends itself to some interesting interpretations.
My first reaction, the more cursory (and cynical) view, is that this is just 'sour grapes' on Coleridge's part, a much more literary version of "Oh, I'd show you! I'd show you all."
But reading it over a few times, there's an undeniable sense of melancholic longing that permeates the whole section. Coleridge really,really, wants to be able to do this. He can smell the inspiration and is tormented by the knowledge of his imperfection as a vessel.
But even if he could, even if he wasn't as horribly flawed as he sees himself as, if for one moment he could write words like music, there's a chance that because of the horribly scattered reading public, his words would fall upon people like his wife, who would plug their ears with religious zeal.