So it turns out Iain Banks asked Ken MacLeod to continue the Culture after his death:
MacLeod said: “He had an idea for the next Culture novel and what he said to me was that he would like me to pick it up and run with it in my own way.
“I was very reluctant to agree even though Iain was insistent that it was something I would write in my own way rather than in a pastiche of his.
“Unfortunately, Iain left not even notes I could work from. If he had managed to get through the summer, he hoped to leave enough notes for me to work from if I wanted to.
As you know Bob, the very first Culture novel was dedicated to Ken MacLeod, so there’s no better person than him who could’ve continued the series. I understand why he’s reluctant to do so, but in this case I’d rather liked to have seen it. But at least Kevin J. Anderson can’t get his hands on it.