This trend should be good for everyone involved, except maybe the blue blood schools.
NBA:
Pros: Gets better assessment of the top kids by seeing them against grown men in the G League. You know some 24 year old that has been grinding in Turkey or Russia for the last 3 years is going to want to show up the highly rated kid. These kids are going to learn what the real world is like, and right quick.
The NBA teams won't have to take as many flyers on freshmen that averaged 12 and 8 just because they are great athletes.
I think that you will see an overall higher quality of play in the NBA because you will have fewer busts.
Cons: The young players will not get nearly as well promoted in the G-League as they would be in college. That is just a fact.
Players:
Pros: Get paid above board for their skills.
Cons: Maybe coaching. The G League coaches may not be focused as much on development as a college coach would be, because the G League coaches are trying to get into the League too and they don't have the leeway to give a ton of minutes to some kid who can't play yet.
Some of these high school stars need a little more time to develop. If they are not ready when they get to the G League, they will be written off pretty quickly.
They will miss the college experience, which is undoubtedly a loss.
Colleges:
Pros: No longer have to deal with the one-and-done insanity. Also, for the second tier McD AA's, not getting invited to the G League will be a reality check for them which should be both motivating and get them to ignore those whispering in their ears to jump early.
The players that go through college will need to be more polished when they leave. Hopefully this will keep the ones that end up in college around for an extra year or two. I hate to see a player do what Tyshon Alexander did.
Cons: Blue Bloods won't have the superstars. Should balance things out a little.