It would extremely helpful if a tool to change the pitch of a video was implemented.
Have you tried using Audacity or similar software to process the audio? Pitch shifting isn’t a feature I’d expect from a video editor like Shotcut, but audio programs like Audacity do it as a standard feature.
+1 for audacity recommendation.
A pitch shift feature is available in Kdenlive, which also uses the MLT backend. However that feature is only available on Linux, so the work needed to port to Windows might prevent this from being tackled by Shotcut developers in exchange for other work on their plate.
A pitch shift filter is not planned officially: https://shotcut.org/roadmap/