All I can find regarding capacity requirements is you need at least 10k seats to host the first weekend of the men’s tournament, you need at least 16k to host a regional and now at least 70k to host a Fiball Four.
There are only 11 sites in the country that meet all the NCAA criteria for hosting a Fonal Four. The bump to a minimum 70k seating capacity eliminated San Antonio, which has them in a tizzy.
I know of no rule that says 33k is not sufficient to host a regional. This past tournament, the four regionals were held in Newark, NJ, Atlanta, GA, Indianapolis, IN, and San Francisco, CA. So two of the four were in traditional ‘small’ arenas much smaller then the JMA Dome capacity.
So 2 of the 4 would not qualify.
In 2026, the regional sites for the NCAA men's basketball tournament will be: South Regional: Houston, TX (Toyota Center); West Regional: San Jose, CA (SAP Center); Midwest Regional: Chicago, IL (United Center); and East Regional: Washington, D.C. (Capital One Arena).
So none of the four would qualify if the minimum capacity was greater than the 33k or so the reconfigured dome now can handle for hoops.
In 2028, the regionals will be hosted in NYC, LA, Kansas City and San Antonio. So only one would have a capacity greater than JMA.
I just don’t think there are enough giant arenas/locations out there to make setting the minimum requirement for hosting a regional to be over 33k.