You have to remember that most hardware acceleration for videos will be based on an assumption that the max frame rate is 60 fps with the most common case being 24 fps for 1080p video.
I suspect a video with such a high frame rate would be blocked from hardware acceleration due to the graphics hardware not being fast enough to do 120 fps decoding and so the cpu would have to do most of the work (at twice the cpu usage of 60 fps video)
In theory a video would work in DeskScapes as it has no internal restrictions that I am aware of but as I say above I imagine performance would be noticably worse than a 60 fps video. Additionally updating the desktop 120 times a second would mean any windows overlapping the video would also have to be redrawn 120 times a second by the OS desktop window manager. With lots of blur this would also use considerable amounts of GPU time.
The purpose of DeskScapes is to run low impact videos and other animated content on the desktop. 120 FPS does not exactly say low impact to me.
