I guess this is a joke, but so as not to confuse new folks, just bypass the cab block, or if you play only acoustics with this preset, don't include a cab block in the first place.
This is not a joke and yes there already is a TOTALLY FLAT cab in Factory 2 1024 location.
Since the late 90s I have used an acoustic pedal called the YAMAHA AG Stomp. While it does not capture IRs of your particular acoustic instrument it does reproduce room environments captured with condenser,dynamic, ribbon,tube and a classical specific microphones. Although I've always had the blend knob all the way up you can adjust how much of the microphone you want. The capture adds depth and space to a piezo or soundboard pickup and smooths away the sometimes unpleasant characteristics of those pickups. This is not the same as using reverb but
with reverb.... it sounds glorious
By capturing an acoustic guitar IR using a microphone you are capturing several things one being the depth and space you get from the microphone which is what is so pleasing. The same can be said by moving a microphone around a speaker cabinet. Using TOTALLY FLAT 1024 I have tried to use the additional parameters in the Room/Air page to fill out the tone but couldn't get it right. I don't know how the TOTALLY FLAT was captured but guessing it's a one fixed point capture.
I agree that using no Cab IR at all would be the same as using a totally flat IR but you couldn't try to use the "goodies " in the cab block.
Using the Null IR could get you to the goodies but to me because of the IR capture and possibly using acoustic instruments it feels limited.
And so enters DYNA CAB with ability to move a mic position approx 10-12 inches away or 4-5 inches L/R from a sound source. This approximates the mic positions used when micing an acoustic instrument. I have tried my acoustic with the 1x10 BF Prince cab with the condenser mic set at 24cm and found that the Room/Air parameters of the cab block now work more effectively to get that depth and space of the YAMAHA AG Stomp.
Now add to that the ability to use a condenser mic as your bridge/body mic and a dynamic mic as your 12th fret mic or any combination with any instrument.
So the options are use the Legacy TOTALLY FLAT with single IR capture and limited results.
Use no cab block but that leaves no "goodies" at all.
Use the NULL IR that gives you back the "goodies" but is once again a single capture and limited results.
Or a
Dyna Cab TOTALLY FLAT Cab IR with the resources to use condenser,ribbon or dynamic mics in a user defined sound source position which allows you to fine tune and enhances the additional parameters on the other cab block pages.
Best case scenario would be a block for acoustic instrument players that captures microphone/room setting that can be blended with the piezo to add space and depth while removing the piezo quack like the AG Stomp. Until then, I would like to see the TOTALY FLAT speaker considered for Dyna Cab conversion for those using amplified acoustic instruments.