Pushing and holding the jogwheel opens up a window on screen, allowing you to select from a number of frames-per-detent selections. Rotate the jogwheel to select one you want, then release the jogwheel and that speed is applied. Turning (not pressed) now goes at the speed you selected. This speed selection menu would also be duplicated in the Util menu somewhere. I like having shortcuts to frequently used things like this, because you're often changing the jogwheel rate several times when reviewing or saving a shot.
Question is, what rates are appropriate, without having too many? I was thinking of something like 1, 2, 4, 16, 64 frames per dentet, and maybe some that are a fraction of the buffer length like NoDak suggested, as the small numbers may not be appropriate when you're saving hundreds of thousands of frames at low resolution. Perhaps from 1/1024 of the buffer down to 1/32 of the buffer per detent.
I think the press-to-hold-select speed you suggest would be even easier if just using "push to open", "Push to close" the settings window, then you don't need the dexterity to actually press-hold-rotate at the same time. As the currently selected "speed" would be pre-selected when pressing, you can always get rid of the settings easily by just pressing a second time if doing it by mistake.
But thinking about it, with the possible exception of single-frame stepping, wouldn't one always want to use a fraction of the buffer length (%) as the speed selection?
For e.g. a total of 5 choices: 1 (fixed), 0.1%, 0.25%, 1%, 2.5%
Then you know for e.g the 2.5% settings, 40 detent clicks will always be the full current range moved?
It would be slightly simpler but always consistent behaviour then. The actual % above probably are good, but real-world experience needed to nail them down - and see if perhaps even just three values would cover the needed use cases, then you could have the even more user friendly:
Jog wheel speed setting
+++++++++++++++
Single-step
Slow
Normal
Fast
(and fine-tune what those settings means so it 'feels' good)