A module to manipulate the pitch (separate from tempo) would make a fantastic & useful plugin. I'm surprised someone hasn't implemented such a control already (to my knowledge). Perhaps there are technical challenges or limitations that I'm unaware of.
I would also really like to see a plugin or some provision that would allow customization of "how much" (% rate) that playback was changed by the hotkeys- similar to how one can customize the length/sizes of the various jumps when skipping back or ahead during playback (although I wish that control would accept 'partial'(fractions of a) second).
I understand that it's possible to start VLC from the command line & specify very detailed playback rates. I'm not sure if the rate can be changed instantaneously via the command line during playback with an accuracy down to 3 decimal points (as described above by a developer). If so, I could use other software such as autohotkey to create scripts activated by shortcuts which would give me a bit more control.
I've tried the slider, it's a great idea, but I've found it difficult, clumsy & unpredictable to use for very fine adjustments to playback speed. Although this could be improved by assigning modifier keys (e.i. shift, control, etc.) that would make adjustments to the slider "fine" or "course" while they were being pressed.
I realize that I am FAR from the typical/average user & that the features I wish for are only likely to be found in high-end, expensive software.