If SF wanted, S^4 could be out way ahead of schedule and we could see devices with S^4 before the end of the year, even Q4. It won't be problematic if they don't release anything at all.
People don't want to get devices with problematic firmwares.
People don't want to chose and learn what "version" will be better for them ("ie S40, S60, S^1, S^2, S^3, S^4) since the devices are not 100% certified to be update-able to the next version/firmware.
The consumers could care less what version the device it has, but they just want to know that their device has the latest version that the company has produced (ie S^4 and not S^3, WM7 and not WM6.5, etc.). In the end, you know that once they get to S^4 they will have to re-write their work to work on the Qt framework/libraries. But we'll see. Hope that S^3 does bring it to the competition, or else it'll turn to WM6.5, uncompetitive. By the time S^4 comes out, iPhone OS 4.0 will be out, as well as Android 2.2 (maybe 3.0?). WM7 will be out next year, so let's see.