- RandR 1.2 support. Support in NVIDIA's binary driver for supporting version 1.2+ of the Resize and Rotate extension within the X.Org Server has long been desired. NVIDIA has said a few times now they are working on it, but it's been years. RandR 1.2+ support within the proprietary driver would allow users to adjust their screen resolution/rotation and other options within their desktop's RandR-based utilities rather than depending upon the nvidia-settings program, which would lead to better and more unified system integration support. With the recent introduction of RandR 1.4, which has some internal changes that may make it easier for NVIDIA to support this X extension, maybe we will finally see proper RandR support in the coming months.
- Optimus support, but NVIDIA has said it's not coming to Linux. However, open-source graphics developers have been working on an alternative though it hasn't received too much attention.
- Kernel mode-setting. KMS support within the NVIDIA binary driver is needed for proper Wayland support, a cleaner virtual terminal, better debugging / problem reporting, and other features. However, it doesn't appear to be on NVIDIA's road-map at this time. There may also be licensing conflicts with a binary graphics driver implementing KMS for the Linux kernel.
Other desired features include game profiles, fan control profiles, and NVIDIA Fermi GeForce 400/500 overclocking support. Read more in this thread.