[The GFX] is the best focus-bracketing system I have used so far.
Really? Don’t you have a Phase XF, which I believe allows you set minimum and maximum focus points? I would think the XF would provide a more accurate approach to the required number and placement of focus points. With the GFX firmware, I think you ( or the camera) are sort of guessing. Can you explain in more detail how the GFX is determining the number and placement of focus points?
Focus Bracketing and Focus Stacking are two separate use cases.
With focus bracketing the goal is to have one master point of focus and capture a couple of safety shots in front or behind that plane of focus. It tends to be most useful in the field and only sometimes useful in the studio. Subject matter movement in between frames is usually not very important. The goal is to capture multiple frames with the intent of selecting the one individual frame that is focused where/how you intended, and saves time fine tuning the focus in situations where time is short or confidence in focus assessment is low.
With focus stacking the goal is to have a front plane and a rear plane, and to capture as many shots (whether that be 2 or 100) required to have focus continuously in between. It tends to be most useful in the studio and is only sometimes useful in the field. The goal is to capture multiple frames which will be combined into one composite frame with greater depth of field. Therefore subject matter movement between frames is often a significant issue.
They are not unrelated (they both involve taking more than one picture with different focus points) but the interface should match the fundamentally different goals of each. You can use a Focus Bracketing feature for focus stacking, but it will be a bit awkward* for it. Likewise you can use a Focus Stacking tool for focus bracketing but it will be a bit awkward*.
If XF users are interested in Focus Bracketing being added to the XF I'd encourage them to share that interest with their dealer or, if they don't have a dealer, by starting a support case at phaseone.com. If there is enough interest it seems simple enough to implement; they have all the technical capability required in the body and have illustrated over and over (FU1,
FU2,
FU3,
FU4) a desire to add tools that are desired by a meaningful part of their user base.
Personally I hope Fuji adds Focus Stacking to the GFX (or future camera) and Phase One adds Focus Bracketing to the XF.
*Awkward doesn't mean unworkable. Just that it's not native/elegant feeling in that use case, especially when compared to the experience of using a feature purpose-built for that use case.