If I understand your concern correctly, looking at our "previous" documentation, there isn't anything about the remember-me attribute in the payload:
https://wiki.jasig.org/display/CASUM/Remember+Me

So, you're right that folks *may* have already customized that attribute name, rather than what's officially specified here. Those can safely be upgraded/ignored, since we are merging on a standard name and adopters can keep the existing name.  

...or were you thinking that there may be a need for "additional" attributes that would describe the remember-me authentication use case, other than just a simple "longTermAuthenticationRequestTokenUsed"?