Michael
Before someone else states the obvious, I would simply say that this has already been requested. You need to be aware of the effort that is put into ML by the developers and, as a stills shooter, I know the video 'stuff' gets the attention.
Having said that, we have dual ISO, extended bracketing and extended DR etc etc. in other words I'm not complaining.
BTW focus steps are linear for macro focus bracketing. It is only when you need to do focus bracketing for landscapes and architectural work that it becomes non-linear.
I for one have written a simple script in CHDK to do landscape focus bracketing.
For my 5DIII, I will wait for the script module to stabilize and then simply implement landscape focus bracketing there, ie on a lens and aperture specific basis.
Also, for wide angles, you really only need 2 or 3 focus brackets, and in this case I simply mark the lens with pre-calibrated focus distances, ie for my 24mm then use 3, 5, and 15 feet.