I've just bought a 930 after thinking the same myself.
My thinking was if there's any upcoming device there would of been leaks and rumours by now. We've heard absolutely nothing.
Give or take a couple of months the 920 came out 2 years ago, in that time, roughly half way we had the 925, which was basically the same device with a few cosmetic changes.
I owned a 925 but only because I hadn't got a 920 when it first came out, if I had, I would of kept that till now and got a 930.
Long story short, the 930 is a great device, there probably not be another 9 series for a year, which if it comes will only probably be an incremental update with probably another year till a '940' becomes available.