That's with cameras like the Hy6 / AFi that use leaf shutter lenses. Almost no movement. M/S backs work very well with cameras like the Hy6 and 6008AF. Focal plane shutter cameras can still work too. It's also an integration thing - some cameras don't talk to the back and software well enough to allow continuous shooting with the mirror up during all the frames and that can lead to movement. However that said, once I had my 6008AF configured incorrectly and the mirror cycled between each of the 19 frames needed for microstep and I was still able to successfully shoot microstep using a modest tripod.
You can get nice images, but you will not get the type of resolution you would get with a tripod that is stable to the micron.
IF one keeps in mind that we are talking about movements of 1/4 of a pixel. That is somewhere between 1 to 2 microns on the subject.
With even a normal lens this means that a movement of 1/10th of a micron of movement left, right, up or down. That is a very very small movement.
You mentioned the Fuji GX 680 that I know very well. It has a very large mirror and it needs to be on a very solid tripod to get the best results even with film.
I particular the GX680 III has more mirror slap than the GX 680. However the GX680 III does not require the photographer to move the mirror up and down manually, but it does slap down and immediately up
after each shutter release.
While I do not use multi shot myself I had long chat with a materials engineer while he was shooting with a Hasselblad Multishot in an industrial setting... I was there to do portraits of one of the execs....
The materials engineer was using the camera to photograph progressive fracturing of high tech composites.
One impact on the composite and then he did several takes and they were inconsistent until he moved over
to using a cut down to size Fatif column stand lowered off the wheels and onto the cement floor. We shot together
for over an hour. I was actually very interested in the materials as I make my own carbon fiber and composite fins for my hollow carbon fiber surfboads that I use for kitesurfing.
Keep in mind he was doing plenty of 100% observation of the files as well as looking at the whole images.
The shots were at about 8 to 10 feet.
He had done comparison tests with regular tripods and the heavy Fatif column to show the difference to his bosses so as to justify buying the
expensive column stand and having it cut down to size to fit in the lab.
The guy was not messing around. Testing materials for chopper blades and jet nose cones.
A similar discussion about how small camera movements (microns) effect false color and Moire came up regarding the d800E.
A wedding photographer said he was getting almost now false color or moire. This was largely due to the fact that he shot hand held.
Even very slight movement was softening his images enough to reduce moire and false colors. With really high pixel densities micro movements that would not have affected us in the past today do.
I also remember years ago at the studio of a very good but slighly nutty still life photographer. Clients like IBM, Olivetti, HP etc.
He loved to blast Deep Purple as loud as hell... he was quite def... but when it came to releasing the shutter the music would be turned off.
Bass in the music was shaking his 8x10 around.