In 2 or 3 years it will probably become mainstream. You won't even see it on a motherboard for a year, and only in the 2011 socket boards then, it will take much longer to filter down to mainstream boards.
Initially, it will be much slower than DDR3, just as DDR3 was slower than DDR2 for several years.
It will have little to no impact on gaming since memory is not a bottleneck for gaming in the foreseeable future.