As long as the quality of the sets remain high and the signature cards are not signers that 98% of the fans could care less about (Figwit and Mark Ordesky) then I think there will always be plenty of demand for the Harry Potter cards. They might not always be the same people, but even if they went to 10,000 boxes in each set there are millions of Harry Potter fans. People will just have to be more selective of which cards they decide to add to their collection and realize they can't have them all. But there are so many more signers possible for the update sets they have to do them:
Daniel Radcliffe .... Harry Potter

Richard Griffiths .... Uncle Vernon
Fiona Shaw .... Aunt Petunia
Harry Melling .... Dudley Dursley
Adrian Rawlins .... James Potter
Geraldine Somerville .... Lily Potter
Lee Ingleby .... Stan Shunpike
Rupert Grint .... Ron Weasley

Chris Rankin .... Percy Weasley
Julie Walters .... Mrs. Molly Weasley
Mark Williams .... Mr. Arthur Weasley
David Bradley .... Argus Filch
Alan Rickman .... Professor Severus Snape

Maggie Smith .... Professor Minerva McGonagall

Robbie Coltrane .... Rubeus Hagrid

Tom Felton .... Draco Malfoy
Emma Thompson .... Professor Sybil Trelawney

Warwick Davis .... Wizard
I don't plan on stopping anytime soon. As long as the updates sets are even close to how good this set is I will be happy. I don't want to see a set like topps FOTR update with a costume card ( or at lease a piece of material that might have been scraps from making the costume) in each box (that can be cherry picked) and nothing else. Just my thoughts on the matter
ztaylork