Although, to address the OP, I would like to see a catastrophic event of some description. Something to bring some new life into the geography.
Heard Pterry speak once. In the Q&A period he was asked if he had any further plans for Esk (Eskarina - the young female wizard in Equal Rites). He said he had some ideas and kept meaning to get back to her.
For myself, I’d like to see some adventures for Sean Ogg. The poor guy gets stuck doing everything.
I like the sports idea. Only Pratchett could give professional sports the send-up they really deserve!
Mort’s dead, remember? Just ask Susan.
Well, you have Theft of Time, which gave us Susan/Nanny Ogg.
Though I can imagine that a Susan and Granny Weatherwax wouldn’t be much – maybe a quick cup of tea, a few short exchanges, and then a “Well, I must be going.”
Start one – you’ve piqued my interest.
And IMO, there are still big chunks of the Disc geography that haven’t been touched, like Howondaland. Or how about a return visit to Djelibabi, Ptraci, and Teppic?
Vimes is fun, but it seems like Pratchett’s been overusing him a bit lately…
(deep breath)
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
No Sports!
NO SPORTS!
I like the idea of Vimes’ story, when he was Brung Low.
In wish I could say ‘Terry, Please, No more childrens books’ because Every time he writes one that’s longer I have to wait for the next ‘grown up’ book. But that would conflict with my full support for the idea of Discworld for children, and… I’m kicking myself for not thinking of Hatfull of Sky and Wee Free Men as presents for my nieces.
I have bought multiple copies of WFM and HFOS for all of my friends children, whether they are old enough for them or not. The books will be there when they can read them. We have to hook the next generation early! 
I have to second Anamika’s “no sports” sentiments! But will disagree with her on her hatred of Susan. Susan rocks. I want Susan’s sense of style, her no nonsense attitude, her ability to stop time. Dear Og yes, her ability to stop time!
I’d quite like to see either more Watch books or more Lancre books – maybe something on how Agnes Nitt is now faring…
Perhaps it’s just me, but I really think it’s time that Unseen University faced competition from an unaccredited rival. Also, the low-budget airlines popping up in Europe could probably provide fodder for a book or two.
Nanny Ogg’s role in Thief of Time was important, but not long. I think having two very stubborn characters butting heads would be interesting. BTW, I agree about no sports. That one could write itself.
I don’t think it’s against the rules to pit fictional characters, is it?
The first Discworld novel I ever read was Equal Rites, which I got as a freebie in my membership pack for the 1988 WorldCon in New Orleans. Ever since then, I’ve wanted to read about the Further Adventures of Eskarina the Female She-Wizardess! (And her loyal sidekick Simon, whose presence in her life just might end up testing the principle of the celibacy of the magy! 
) I mentioned this to Pterry at a panel discussion at the 2003 WorldCon in Toronto; he replied that he couldn’t make any promises, the stories happen when they happen.
A turtle’s ventral carapace. See The Last Hero, in which Carrot, Rincewind and the Librarian fly a spaceship (invented by Leonardo da Quirm, of course) to the Gods’ home at the Hub (Dunmanifestin), stopping by the Moon on the way. They get a good look at the Discworld from space – and so do we, thanks to Paul Kidby’s illustrations! 
He has been doing more with the Igors. I think that there is a whole book there. Maybe Igor and Reg? That would be interesting interplay. No, I have it. Igor and Doughnut ?Willie (the horsedoc) starting a hospital in A-M.
Read Going Postal yet? There’s already a new hospital in A-M . Wouldn’t surprise me if it gets developed further in a future book.
And speaking of Discworld geography (discography?) I’ve thought for a long time that Pterry might do something someday with the Muntab Question.
We’ve already got Granny Weatherwax and Nanny Ogg for that.
Susan’s big thing is against incompetent idiots. Granny, being far from incompetent and in no way an idiot, would make a terrible foil for her.
His next book is called “Thud!”.
The Discworld fans recently created a Discworld game, I think it’s a sport of some kind, called “Thud!” which was invented long before this upcoming book was known about.
My guess is that “Thud!” may indeed be about sports.
Personally I want to see what happened to Eskarina Smith, who if we judge by Susan’s aging (and I’m not sure if we should, as she and Time don’t seem to travel in the same circles), should be around 25 years old now, and I wonder if maybe she’s caught the eye of one Ponder Stibbons…
The L-Space Timeline puts Equal Rites in 1964, and Last Continent (in which IIRC Ponder is about 24) in 1988. So she’s probably eight or nine years older than Ponder. Nice thought, though.
They were not the first to make the trip, remember. Some poor soul fell around the bottom, and on returning said “My god, it’s full of elephants!”
My favorite pTerry line.
I didn’t know somebody had constructed a timeline. Interesting.
No mention of Small Gods though. And is about 15 years since the last update.
I tell a lie, there is mention of Small Gods. In what has to be totally the wrong place.
It should be at least a hundred or more years before the main novel timeline.