Let's begin with the largest media markets in the US that are currently without the NBA:
21 St Louis
28 San Diego
30 New Haven/Hartford
31 Kansas City
Three common stumbling blocks stand in the way of many of these cities and I will use them to narrow down the list. The first is proximity to a current NBA franchise and the second is competition with a NHL franchise. The third is proximity to a dominant NCAA program.
Using the first qualifier---
Tampa is too close to Orlando. Raleigh/Durham is too close to Charlotte. Baltimore is too close to Washington. While San Diego is two hours away from LA, Southern California is already saturated and unless the Clippers were to return or the Kings left Sacramento I don't think it would work. Nashville is too close to Memphis. New Haven/Hartford is too close to the Knicks, Nets, and Celtics to succeed.
Using the second qualifier---
Tampa has the Lightning. St Louis has the Blues. Pittsburgh has the Penguins. Raleigh/Durham has the Hurricanes.
Using the third qualifier---
Pittsburgh has both Pitt and Duquesne vying for attention. Raleigh/Durham is in the heart of Tobacco Road and arguably Charlotte's lack of success can partially be attributed to the dominance of college basketball within the state. I left Columbus and Cincinnati off my initial list (both are in the low 30s market wise) but they won't work either due to Ohio St and crosstown rivals Cincinnati and Xavier. Columbus also has the NHL Blue Jackets working against it and NBA fans in the city are already loyal to the Cavaliers.
This leaves Seattle and Kansas City. Kansas City has the Sprint Center already in place and could host an NBA team immediately. Seattle recently lost the Sonics because ownership wanted a fancy new stadium that the tax payers weren't prepared to bankroll but one could be built to support NBA and/or NHL if a team was promised to the city.
Aligning 32 teams
Rather than doing 6 divisions of 5/6 and have uneven divisions I think the solution is 4 divisions of 8. 8 divisions of 8, like the NFL, would split up too many rivalries. I devised a 4 divisions of 8 with only splitting up one rivalry and only putting one team in a somewhat odd region.
Pretty straightforward. Everyone but Utah is on Pacific time accept Utah. I hated to separate Utah from Denver but it couldn't be avoided--this was the least destructive move I could make. My thoughts were that Utah and Phoenix would become a rivalry game. Historically, this move restores Portland and Seattle to a division with the California teams and Phoenix where they played from 1970-2004.
Of my four divisions I like this one the least. Denver is kind of an odd ball but Denver is essentially a huge city in the middle of a mountain range--there isn't anyone that is really close to them. On the bright side, Denver was in a division with the Texas teams for 24 years from 1980-2004 and is an ABA legacy like the Spurs. There's also a chance that they can build some animosity with the Thunder who are a young franchise without a real rival (however the citizens of Seattle will hate OKC for eternity). Atlanta is a bit of an outlier too but to best fit everyone in they work the best here. This division at least contains two other Deep South cities--Memphis and New Orleans, that they could learn to dislike. Yes it spans 3 time zones but 6 of the teams are in Central so its only really an issue when Atlanta and Denver play each other.
Here I created a true Midwestern division. The Timberwolves are at long last with teams that make geographic sense rather than the old haphazardly designed Northwest Division. Newcomer Kansas City fits in well and Toronto isn't too odd an addition either with its proximity to Detroit and Cleveland and Toronto was with many of these teams from their founding in 1995 until the 2004 realignment. The NBA could even try to piggyback the NHL schedule by making Raptors-Pistons the day before/after Leafs-Wings games.
I pretty much subtracted a team from two existing divisions and then shoved them together but I did so with a rhyme and reason behind it. Washington is culturally northeastern and not southern so it made more sense for them to be with Boston, New York, and Philadelphia. Also, Florida and Charlotte are populated by a lot of northern transplants. The NHL used a similar logic when they devised their yet to be adopted 4 division model. The players' union blocked it
The quick and easy solution would be to to just designate two divisions as one conference (American) and the other two another (National) and stick to the same model that currently exists. However I'm going to take another page from the NHL proposal and suggest the playoffs take on a more divisional flavor. The top four in each division make the playoffs and are seeded such that 1 plays 4 and 2 plays 3 in a seven-game series. Winners advance to a Division Title Series. Winners of the four Division Title Series advance to the NBA Final Four Series, a seven-game series, where seed is determined by regular season record. Naturally, the winners of the two Final Series then meet in a seven-game Title Series.