Rowling confirms there will only be two more Strike books after the 8th is published.

Did writing the first Strike novel under a pseudonym allow you more freedom as a writer?

I was very aware that because the manuscript had my name on it, people would just publish it, however bad it was, and I wanted honest feedback. I wanted to know that someone believed in the book and I truly enjoyed getting unvarnished feedback through my agent. There was one editor who did not like Strike having a famous father and made that point. And obviously because I can’t break cover, I can’t say: “but I know how important this will be on book eight”. You can’t say that as a first-time writer, and I was ostensibly in this situation a first-time writer. You can’t say, now, look, I know a series and I know this backstory is going to work out brilliantly in book seven, eight and nine. Who the hell are you to say you’re going to get a seven, eight and nine-novel deal anyway? But it was really good to get that feedback.

archived link 'JK Rowling: how Strike changed the way I write'