It'll never happen. At best what you're gonna see is one D-League team per pro squad. The NCAA ultimately wouldn't be the competition if we're talking about a true minor league. The overseas leagues which have better competition and pay better are the biggest hurdle. Also keep in mind, the D-League is meant for guys on the come up (in other words, a team couldn't send a vet down if they wanted to).
Last CBA had conditions for NBA sending players to the D-League though, if I remember correctly. I think it had to be approved by the player and they had to get called back up.