Yep, "Happy Families" (working title) a.k.a "Dodger" (a new working title https://twitter.com/#!/terryandrob/status/134577693336412160
) is a Victorian era novel in the same/a similar universe as "Nation". That's next year's novel in addition
to The Long Earth.
"Raising Taxes" is potentially the next Discworld (Moist) book /after/ those two, but I don't think Terry's started writing it yet.
He's currently working on The Long Earth, Dodger and his autobiography.