According to what stated on Twitter from @MrXBob , was issued an update to members of the Xbox Preview programme One whereby you can record movies at 60 frames per second using Game DVR. The same MrXBob has already shown some movie, noting that at the moment is you can record at 60 FPS, but that processing the videos Upload Studio the same will return to 30 FPS. You can see some examples here , here and here

Another user who has received the update (Max Tremblay) has posted a video on youtube, as well as on his Xbox profile ; You can see it at the bottom.

The ability to record movies at 60 FPS is one of those capabilities requested loudly by most users, and eventually Microsoft decided that it was time to oblige. At this point, we just have to wait for the official announcement from Microsoft and try to figure out in which month will be released to everyone. Keep checking back for more updates.