Columbus would never get a team. Too close to both Cleveland and Indianapolis. Cincinnati or Louisville are much more likely from that region. St. Louis would seemingly make the most sense outside of Vegas (which I agree wouldn't happen).
So assuming you add St. Louis and Seattle this would be how I would draw up the divisions
1 - Seattle, Portland, Sacramento, Golden St.
2 - LA, LA, Phoenix, Utah
3 - Denver, Dallas, Houston, San An
4 - Oklahoma City, St. Louis, Memphis, Minnesota
5 - NY, Brooklyn, Boston, Philly
6 - Milwaukee, Chicago, Toronto, Detroit
7 - Miami, Orlando, New Orleans, Atlanta
8 - Washington, Charlotte, Indianapolis, Cleveland
I would set it up so you play the other 3 teams in your division 5 times, the other 12 teams in your conference 3 times, and the 16 teams in the other conference twice, for a 83 game schedule (rotate years on the extra home vs. extra road game). If they wanted to keep it an even number, play the other teams in your division 6 times and go to a 86 game schedule. That sort of set up would really put more emphasis on the divisions and would really foster the rivalries more.