"testability" and "threshold" issues for cognitive -- and how to solve them?

Since my last email ws TLDR  -  let me repost a part of it separately 


I DO agree - that we there are critical things that are needed by people with cognitive disabilities that we have not been able to figure out how to make requirements for.  
Testability and threshold are both problems that have prevented us from having more requirements.
(The whole reason I  am working on WCAG 3 in retirements is that I am trying to figure out how to get more good guidance for people with cognitive disabilities into WCAG 3.    
And I  am also in my retirement working on an alternate approach that would be really great for people with cognitive disabilities.   One that would remove/solve both the testability and threshold issues. 

By “the threshold issue" I  mean the following.   
Just for discussion sake, let's say all people with intellectual disabilities, fell into five levels. 
If we could find a measure of simplicity (of text for example)...
which level of simplicity should we require  (what level of simplicity would be what was required?)
If you said 3, then people who were 4 and 5 would have to use text that was simpler than what they need (and they would have to be losing the information between level 3 and the level they were able to handle. 
And the content would still not be simple enough for people at levels 1 and 2. 
So do we discriminate against levels 1 and 2 and leave them behind?  (and simultaneously force levels 4 and 5 to use oversimplified text?)

Also, (as we have all experienced) once we understand something at a simple of a we can often understand it at a more complex level. How many times have you not understood something until someone said "let me give you a simple example”.   Then, once you've seen a simple version of the concept, the broad or more complex idea they were trying to express is suddenly clear. 
Thus, even for a single person there is no correct level of simplicity. 
There is the level that is needed for them to understand something new, 
and then there is a different level that they can handle once they understood it at the simpler level or if they are already familiar with the concepts.

I suggest that a much better approach 
is to work to have it so that each user can adjust both the language level — and in level of inteface complexity - to whatever level they need.
and this would be done at the user agent level (browser or AT) so that it could be set by the user and used across websites
and would allow users to select the type of interactors that they prefer and have consistency not just in a website but across websites

I think we should push for smart assistive technologies or smart browsers 
that can take whatever the content is on the page and present it to the individual at whatever level they need to be in order to be understood. 
This would not only eliminate the need for us to have a "testable" level of readability or consistency (which I think we will never have) 
but also eliminate the threshold problem described above. 
It would allow individuals to be able to adjust the text to whatever level works for them. 
Moreover they could do it dynamically 
so that they would only have to ask for simpler versions of pages that they had trouble with, 
and would only have to simplify sites as much as they needed to to understand it. 
Also, as noted above, once they understand the site basically,  they may be able to turn the complexity up to a higher level and still understand the site more completely.

This is the equivalent to having AT for someone who is blind or has low vision 
and has the ability to adjust the magnification to what they need but not more 
or to adjust the reading speed or other factors to be matching what they need but no more.