The 4S will most likely follow the path of the 3GS in terms of support. The 3GS has been through 3 and a half iOS's of support, with a lifespan of years this coming June. The 4S parallels the 3GS in terms of popularity and hardware potential. Like the 3GS now, the 4S a few years down the line would still be a great device, but will of course be overpowered by other devices of the newer generation.