This was the NBA in the 1975-76 season, the last before the merger with the ABA:

Eastern
Atlantic - Boston Celtics, Buffalo Braves, Philadelphia 76ers, New York Knicks
Central - Cleveland Cavaliers, Washington Bullets, Houston Rockets, New Orleans Jazz, Atlanta Hawks

Western
Midwest - Kansas City Kings, Chicago Bulls, Milwaukee Bucks, Detroit Pistons
Pacific - Golden State Warriors, Los Angeles Lakers, Phoenix Suns, Portland Trail Blazers, Seattle SuperSonics

The surviving ABA teams were the Denver Nuggets, San Antonio Spurs, Indiana Pacers, and New York Nets. Denver and Indiana join the Midwest, the Nets join the Atlantic, and the Spurs join the Central.

But what if the NBA adopted an AL/NL type alignment?

American
West - Denver, San Antonio, Golden State, Seattle, Milwaukee, New Orleans Jazz
East - New York Nets, Indiana, Detroit, Washington, Buffalo

National
West - Phoenix, Houston, LA Lakers, Portland, Chicago, Kansas City
East - New York Knicks, Cleveland, Philadelphia, Boston, Atlanta

The New York Nets would move to Jersey before the start of the 1977-78 season.

In 1978, the Buffalo Braves move to San Diego and become the Clippers. They trade divisions in the American Conference with Milwaukee.

In 1979, the New Orleans Jazz move to Utah, but remain in the American West

In 1980, the NBA adds the Dallas Mavericks. They join the National West, moving Chicago to the National East.

In 1984, the San Diego Clippers relocate to Los Angeles, but remain the American West.

In 1985, the Kansas City Kings relocate to Sacramento, but stay in the National West.

In 1988 we begin seeing more substantial deviations from the present timeline. Charlotte joins the American East, while Miami joins the National East. The following year, the Orlando Magic join the American East and the Minnesota Timberwolves join the National West.

American
West - Denver, San Antonio, Golden State, Seattle, LA Clippers, Utah
East - New Jersey Nets, Indiana, Detroit, Washington, Milwaukee, Charlotte, Orlando

National
West - Phoenix, Houston, LA Lakers, Portland, Dallas, Sacramento, Minnesota
East - New York Knicks, Cleveland, Philadelphia, Boston, Atlanta, Chicago, Miami

Miami and Charlotte temporarily spent time in the Western Conference in real life as the NBA attempted to balance the expansion teams' effects on both conferences.

In 1995, the Canadian expansion happens and the NBA realigns to six divisions:

American
West - Golden State, Seattle, LA Clippers, Vancouver Grizzlies
Central - San Antonio, Denver, Utah, Milwaukee, Indiana
East - New Jersey Nets, Detroit, Washington, Charlotte, Orlando

National
West - Phoenix, LA Lakers, Portland, Sacramento, Minnesota
Central - Chicago, Cleveland, Houston, Dallas, Toronto
East - New York Knicks, Philadelphia, Boston, Atlanta, Miami

Following the 2000-01 season, the Grizzlies relocate to Memphis.
They move to the American Central, while Denver and Utah move to the American West.

The Charlotte Hornets relocate to New Orleans in 2002, but no division changes happen.

In 2004, the Charlotte Bobcats (now Hornets) are added to the American East. The New Orleans Hornets (now Pelicans) move to the American Central.

American
West - Golden State, Seattle, LA Clippers, Denver, Utah
Central - San Antonio, Milwaukee, Memphis, New Orleans Hornets, Indiana
East - New Jersey Nets, Detroit, Washington, Orlando, Charlotte Bobcats

National
West - Phoenix, LA Lakers, Portland, Sacramento, Minnesota
Central - Chicago, Cleveland, Houston, Dallas, Toronto
East - New York Knicks, Philadelphia, Boston, Atlanta, Miami

In 2008, the Seattle SuperSonics relocate to Oklahoma City, but remain in the American West.

In 2029, the NBA expands to Seattle and Las Vegas, prompting s move to eight divisions. Phoenix and Utah swap conferences.

American
West - Golden State, LA Clippers, Seattle, Phoenix
South - San Antonio, Memphis, New Orleans Pelicans, Oklahoma City
North - Milwaukee, Denver, Indiana, Detroit
East - Brooklyn Nets, Washington, Orlando, Charlotte Hornets

National
West - Las Vegas, LA Lakers, Portland, Sacramento
North - Chicago, Minnesota, Cleveland, Utah
South - Houston, Dallas, Atlanta, Miami
East - New York Knicks, Philadelphia, Boston, Toronto

By 2031, both North divisions are fed up with spanning three time zones. Minnesota and Cleveland move to the American, while Denver and Milwaukee move to the National.

American North - Indiana, Detroit, Minnesota, Cleveland
National North - Denver, Utah, Chicago, Milwaukee

Touche. I've done something like this before, but moving from a more logical alignment to less logical one doesn't hold as much appeal.

Doing the NHL next?

It was such an unequal merger—the NBA was so much larger, that a complete rearrangement makes little sense. Squeezing the ABA teams into the existing structure was the most logical move.