"no one"!? Big Ten's AAU standard has not changed. UNL joined the AAU 107 years ago. Unfortunately it ranked at the bottom of the AAU's members for more than a decade based on the AAU ranking system which ranks all research universities. That ranking system consists of four criteria: research expenditures, National Academy members, faculty awards (from a specified list) and citations. They were actually invited and accepted into the Big Ten months BEFORE the AAU dismissed UNL in April 2011. I recall the chancellor at UNL stating that they would never have been invited to the Big Ten if they weren't AAU to begin with despite being voted against by Mich. and Wis.
However, it's important to note that research institutions in the AAU do not have the same ranking percentage weights that typically determine the overall academic standing of colleges and universities throughout the nation. Criteria are weighted based on the number of tenure-track faculty, graduation and retention rates, alumni support, student selectivity, etc. Based on those criteria, even a number of non-AAU institutions ranked higher than over 15 of the 63 AAU institutions, including UNL during their AAU membership period.
Notre Dame's lack of AAU membership didn't stop the Big Ten from trying to grab them a number of times, because of all the other strengths Notre Dame brings to the table. ND has a sterling reputation in undergrad education and since 2010 has made a significant push to become a leading research and graduate university. Notre Dame would probably love to be an AAU member to solidify its status but becoming a member is by invitation ONLY. They have not been invited yet, but could be in the very near future. I see no problem with ASU being accepted as a sport affiliate member in men's ice hockey based upon its academic reputation, despite being non-AAU.
AAU Members