My own list:
- GPU acceleration. Gaming is a non-goal (games do a bunch of stuff, like anti-cheat, that interacts badly with Qubes), but CAD, video editing, and possibly GPU compute are in scope.
- Reduced RAM usage.
- Faster boot time.
- Lower audio latency
- Nested virtualization
- Nested IOMMU
- Qubes-in-Qubes (for testing, if nothing else)
- Wayland native, no more X11
- GUI daemon draws its own decorations
- virtiofs-based file sharing
- Secure browser that runs each origin in a dedicated microVM
- Hardened sys-usb that is secure against malicious USB devices
- Hardened sys-net
- Hardened malloc() everywhere