Again, John, you're missing the point. ALL seams must be covered either with KerdiFix, or the proper overlap of Kerdi or Kerdiband. If you do this with a modified thinset, the laytex component will allow wicking, whereas the proper consistency of a good dryset, where the excess is squeezed out while embedding the membrane will prevent wicking, typically less than 1/4", and way less than the specified 2" minimum overlap. Since the layer of unmodified thinset is quite thin, it won't wick much in any reasonable timeframe, maintaining the waterproof properties of the SYSTEM. ANY other testing or procedure will potentially allow moisture to seep into the edge and affect the backing material. Do not use drywall mud, at least the non-setting type, underneath Kerdi. The moisture from the thinset can soften it. Keep in mind also that like any mortar based product, it doesn't set immediately. The next day, you could likely easily peel the sheet off the wall. But, try that after a week, or the specified 28-days for stated strength of any mortar, and you'd tear the fleece off the membrane, if you could get it off. After a short time, the grip is still quite good, and sufficient to set your tile, it just gets stronger after time. The fleece is, I think, required to hold 50psi in shear to pass the tests, and when tested showed 75psi. These specs and test material are in the handbook. The Kerdi membrane covering the whole seam in drywall is MUCH stronger than the tape, and is all that is required to tie the two sheets together. You do not want or need drywall corners if it is going to be covered with tile. If you did use them, you'd need to affix the Kerdi with Kerdifix, as thinset is not approved to hold Kerdi to metal.
Anyone can devise a test and prove anything can fail. But, Kerdi, when properly installed AS A SYSTEM, creates a waterproof shower. Properly seal your seams, and you won't get moisture beyond approximately 1/4" into the seam which still has about 800% backup before it could create a problem.
And, consider that in a properly completed shower, there is VERY little to no constant liquid water underneath the wear surface, the tile. It won't accumulate if your slopes are proper (and would still be waterproof if it didn't). So, since the migration and waterproofing is done with standing water in a flood test, as long as you don't penetrate the seams, once tile is installed, you're golden. Like anything, quality of craftsmanship and proper adherance to the manufacturer's instructions yields a successful result. Miss a step, and it can fail. But, the golden, simple rule with Kerdi (and any sheet membrane) is, verify proper embedding of the fleece to the backer, and make proper seams.
Schluter has 35-years of experience with this product and the technique to install it properly is described in their manual. The approval agencies all specify that it must be installed per the installation manual. Do it that way, don't try to improvise, and it works. The system is quite flexible. If you can install wallpaper, you have a high probability of succes, assuming you can read and follow instructions. As good as (and in my opinion a better chance) of any other system out there in a successful install.
I'm at my sister's now, trying to fix some supposedly pro tile installs...rotten subflooring, broken tile, nasty. Not all pros are that. They broke a lot of rules in this house and she's now paying for it. One would hope in a $600K house that wouldn't be the case. Do it right, and it works. Do it wrong, and you may be lucky, but it will probably fail...true for anything. 35+ years of field experience in the USA says Kerdi works.