<<< I had definitely hoped for some new light to be cast on the story or characters of the New Sun - else why bother with them? >>>
Half-serious two-a.m. speculation: is it at all possible that the Whorl's next destination is Urth itself? If that were the case, it would go a long way towards washing the Red Sun passages of their vaguely unhealthy, fanficcy air ("Oooh! It's Severian! Oooh! It's the Samru! Oooh! It's Abaia!" & so on.) Certainly the idea lends a new cachet to RTTW's title. And consider: the Whorl would return to a very Blue-like (and mostly empty) planet, ripe for repopulation. Perhaps this has something to do with Horn's bargain with the sea-monster Scylla. Perhaps Horn's spirit is on Urth, and perhaps that's why Nettle decided to leave.
And perhaps I'm just a loon....
Jacob G Corbin
*This is WHORL, for discussion of Gene Wolfe's Book of the Long Sun.