In an interview with Guitarist Magazine, Rush guitarist Alex Lifeson had this to say:
"Originally the plan was to get back into writing and then recording this year but this tour was so successful with the demand for us to carry on and play a little bit longer. So we played with the ideas and as we got closer to the end of the tour we realised we were going to get a lot of push to continue it. And we wanted to, we didn't think we were going to have quite as much fun as we've had with it.
So Ged and I will get back to writing in the new year. We'll get through the Christmas holidays and start writing through January and February. We only have two or three more songs that we feel we need for the album. So we can start reworking the material and get it in great shape. Then we'll prepare for the tour in March, finish in July, take the summer off then start work in earnest in September."
You can read the entire interview at Guitarist Magazine.