That will never happen. Why would we have 30 D-League teams? The best case scenario is to have 3-4 teams split D-League teams. They won't necessarily get to learn the offense of each team, but they will have 3-5 D-league players.
It isn't optimal, but there is no way when we have rosters of 13 players in NBA that they are going to spend time and money developing another 12-15 players with the hopes one makes it to the bottom of the bench.
There are currently 18 D-League teams, and of those 18 teams, 17 of them are either owned or operated by an NBA professional team.
Here are the teams where the NBA team currently owns their D-League team:
San Antonio Spurs
Oklahoma City Thunder
Los Angeles Lakers
Golden State Warriors
New York Knicks
Cleveland Cavaliers
Philedelphia 76ers
Here are the teams where the NBA team is the single affiliate (runs basketball operations) for the local D-League team:
Sacramento Kings
Boston Celtics
Houston Rockets
Miami Heat
Dallas Mavericks
Memphis Grizzlies
Phoenix Suns
Utah Jazz
Orlando Magic
Detroit Pistons
So currently over half the league (if just barely) either owns or operates their D-League club, so we are more than half-way to the point where every NBA team has some sort of stake in a single D-League team.
As an organization the Spurs have been the model franchise and were the 2nd NBA team to actually purchase a D-League team with the Lakers being the first NBA team to do so.
If you're the Spurs, there is a huge advantage to teach/run your system on a minor league team to see if players that you like can actually pick it up and play it the way that you might hope.
To take a current example, it would be great to be able to sign Moreland to the Bighorns and see if he does have what it takes to play the weak-side defender role in the offensive and defensive schemes that your club runs, and if he does he is fast-tracked right onto the Kings team after they clear a roster spot for him. All with-out having to worry that another professional club will scoop him up just as you've finished developing him on your minor-league team.
Developing players in the D-league would mostly be for support/role players. Looking for the 3-and-D players, the shot blockers, the dirty-work players. Players that can both fill the role AND run the offensive/defensive schemes of your professional team.
The NBA would be well suited to modify the entire D-League structure to become a minor league farm system for the professional teams.
I am hoping that something like that is realized in the next 10 years or so.