The G30 gives better color out of the camera than the 920, and the 920 is a little sharper. The G30 also provides full manual controls as well. If you want a simpler camera, then the Canon 500/50/52 models have a similar image and are a lot cheaper than either the G30 or 920. In Canada the MRRP for the 50 is $400, and the 52 is $450. I am not sure what the price for the 500 is, but probably is less than that.
Canon updates their consumer video cameras on average once a year, but there have been longer intervals. The G30 was released a few months after the G20, so the release interval was much, much shorter in that instance. I think it is likely that Canon will release high end consumer equivalents of the new 4K and 2K Sony cameras sometime this year however, but you can never be sure.
If you were thinking of the G30, personally I would wait since it is quite expensive and I have little doubt that much better cameras will be on the market at that price point sometime this year. If you want something now, and have modest requirements for using it, then the Vixia HF 500/50/52 range might do, or the Panasonic 920 (which is a four or five hundred dollars more expensive).