This morning I was on BBC Breakfast discussing Capaldi's casting, sharing the famous red sofa with Sophie Aldred, who played companion Ace in the late 80s (pictured, pic courtesy of BBC). Sophie thought back to the 25th anniversary, commenting that in those days you could barely buy a Doctor Who mug, let alone the sonic screwdrivers, action figures, books, audios and countless other bits and bobs that modern day fans take for granted. Can you imagine Sophie's Doctor, the redoubtable Sylvester McCoy, being unveiled on a live prime time show with celebrity fans and ticker tape? The Doctor Who circus is definitely in town in 2013.
And why not? Doctor Who has been stretching kids' imaginations since 1963 and is a slice of proper family entertainment in the 21st Century.
What does Capaldi's casting mean for the show and its related consumer products? At the moment, we just don't know. The 12th Doctor will make his debut on Christmas Day and until then will be a mystery. Capaldi, the oldest actor to play the role since William Hartnell, may bring an edge to everyone's favourite Time Lord. Like Tom Baker before him, he could be a more alien figure. But he could also be as funny and charming as his predecessor Matt Smith. Capaldi is a consummate comedian - and the Doctor has always liked a laugh. That's the exciting part of being a Doctor Who fan. You just can't tell what's coming - and that's what makes the show unique.
Doctor Who has change and renewal hard-wired into its DNA. Every since William Hartnell's First Doctor complained that his old body was wearing a bit thin and regenerated into Patrick Troughton, the show - and its myriad spin-offs - have changed with the times finding new fan-bases, sometimes losing people along the way, but constantly attracting new generations.
However, when Mark Wright and I were researching our official Doctor Who miscellany, Who-ology, the one thing that became obvious was that the more things change, the more things stay the same. The Doctor may change his face and his companions, but he's by and large the same man. Fans have 'their' Doctors, but they largely stay on board the TARDIS even when a fresh pair of hands are at the controls. What a new Doctor gives us is a jumping-on point. Expect a host of books, toys and packed-lunch boxes emblazoned with Capaldi's face come 2014.
The great thing is that it's not a case of out with the old, in with the new. Sophie Aldred played Ace during the 25th anniversary in 1988. She's still playing Ace in official audio dramas produced by Big Finish. A new range of ebooks is coming featuring past Doctors from BBC Books, and shops around the world will no doubt continue selling merchandise featuring the faces of Jon Pertwee, Peter Davison, Colin Baker and the rest. The new Doctors live side-by-side with the old. How appropriate for a time traveller.
There's no need to worry that people will stop buying current Doctor Who stuff, just because a new incarnation is around the corner. Doctor Who has a legacy that continues to grow year on year. Every child (and adult) who experiences Doctor Who for the first time through Capaldi has 50 years of entertainment to experience and a bunch of sonic screwdrivers to collect. And boy, do Doctor Who fans like to collect (says that man who still has the cards given away by Weetabix in the Seventies).
The challenge will be to live up to that long legacy - to continue making books, audios, toys and merchandise that are worthy of carrying the Doctor Who logo. The buzz around the new Doctor can only revitalise the brand - get it right and the products you produce will have just as much a place in Doctor Who fans' hearts as the show they love.
Cavan Scott is the co-author of Doctor Who Who-ology, out now from BBC Books. You can find him at www.cavanscott.com.