J K Rowling (aka Robert Galbraith, of course) has said at the Harrogate Crime Festival that there will be more than 7 books in the Cormoran Strike series 
. I loved the first in the series and have got the second on my Kindle to be read shortly, and it looks like we could have a new one to look forward to every year or two for the foreseeable future.
This is from the BBC website. (And I love the fact she has a special suit for her alter ego!)
JK Rowling plans crime book spree
JK Rowling wore 'my Robert suit' to discuss her alter-ego Robert Galbraith
JK
Rowling's crime novels written under the pseudonym Robert Galbraith will
eventually outnumber her Harry Potter books, she has revealed.
The author said her plans as Galbraith were "pretty open
ended" and that his books would number more than the seven Harry Potter
novels she wrote.
The second novel under Galbraith's name was published in June, and she said she was half-way through writing the third.
She was speaking at a rare public talk at Harrogate's Crime Writing Festival.
Galbraith's novels follow
private detective Cormoran Strike, a former military police investigator
in the Special Investigation Branch.
Rowling, who began using the pseudonym for her crime writing
career after completing the Harry Potter series, said the third Robert
Galbraith novel would centre on returning military personnel.
"The next book is quite different," she said. "You find out
quite a bit more about what happens to people after they leave the
military."
Rowling and Val McDermid appeared in front of fans at Harrogate's Royal Hall
Rowling was interviewed on stage in Harrogate, North Yorkshire, on Friday by fellow crime author Val McDermid.
Asked whether it was true that she would write a total of
seven novels under the Galbraith name, Rowling replied: "It's not seven.
It's more. It's pretty open ended.
"I really love writing these books, so I don't know that I've got an end point in mind.
"One of the things I absolutely love about this genre is
that, unlike Harry, where there was an overarching story, a beginning
and an end, you're talking about discrete stories. So while a detective
lives, you can keep giving him cases."
She added: "I'm about half-way through the third [novel] and I've just started plotting the fourth."
Wearing a grey suit and pink tie, which she described as "my
Robert suit", Rowling told the audience that she started writing under a
pseudonym because "I wanted to prove to myself that I could get a book
published on the merits of the book".
The author's true identity was revealed last July, three
months after Galbraith's debut novel The Cuckoo's Calling was published.
"While it lasted, it was a lot of fun," she said of the pen name.
The follow-up, The Silkworm, was published last month.
Asked why she chose to write crime stories after the Harry
Potter series, she replied: "I love crime fiction. I've always loved it.
I read a lot of it and I think, in many ways, that the Harry Potter
books are whodunnits in disguise.
"I enjoy, I suppose, the 'golden age' book. That's very much
what I was trying to do in these books - to take that finite number of
suspects, the genuine whodunnit style, but make it very contemporary,
bring it up to date, and make sure this is a credible person with a
credible back story for nowadays."
Referring to the "golden age", she said she was a fan of
authors Agatha Christie, Dorothy L Sayers, Margery Allingham and Ngaio
Marsh, who wrote in the mid-20th Century.
"My very favourite of those four is Allingham, and she's the
least known," she said. "The Tiger in the Smoke is a phenomenal novel."
Rowling is also currently working on her first film script, for Harry Potter spin-off Fantastic Beasts and Where to Find Them.
"It's been challenging, it's been fascinating, it has been a
lot of fun," she said of script-writing. "But as fun as it's been, my
first love is definitely novels."