The plan is reportedly to make S Mode available for most versions of Windows 10 (with new Core+ and Workstation variants being the exceptions). The cost of unlocking full access would depend on what you're running: Windows 10 Home S users could unlock to the regular Home release for free, while those using Windows 10 Pro S would have to pay the previously mentioned $49. You wouldn't be forced to cough up cash just because that 10 S PC you bought feels too restrictive.
There's no firm timetable for when the switch would happen, but Thurrott understands that a shakeup of Windows 10 prices for partners, which includes S Mode, will take effect between April 2nd and May 1st. We've asked Microsoft for comment and will let you know if it can confirm any details.
This isn't necessarily a rejection of Windows 10 S as a concept, although data in the documents suggests it has had a mixed reception. About 60 percent of users with third-party 10 S PCs stick to the software, but 60 percent of those who switch do so immediately. In other words, people who buy Windows 10 S machines usually know what they want. The problem, as you may have noticed, is that these are third-party computers -- it's likely that Microsoft's own Surface Laptop would skew the numbers. A shift away from a release could be an acknowledgment that 10 S works better as a settings toggle than a separate product.