Well RFOM was released in November 2006, Ratchet & Klank in November 2007, so it would sound right if it was released in November 2008.
Insomniac have been developing on the PS3 for 2-3 years now. I very much doubt that they have waited until R&K has gone gold before starting work on RFOM2. I wouldn't be surprised if there was a small team working on it since RFOM was released at the end of 2006.
We will probably start seeing screens from it well before the summer and I fully expect it to be released in late 2008.
Prediction (June 12th 2017)
Permanent pricedrop for both PS4 Slim and PS4 Pro in October.
PS4 Slim $249 (October 2017)
PS4 Pro $349 (October 2017)