The only juniors I am aware of that have a shot clock, at least in Victoria, is at VJBL level or higher, never at domestic level. Maybe in a tournament and of course at things like Nationals.
So, at juniors I see no problem at all, interesting thought to allow 8 seconds then 24 in the half court, but too hard to manage one would think, officials don't always get the 8 seconds right and how do you manage something like two different time sets in one sequence of play?
In the NBL I have enjoyed some of the high octane offence and fast pace shooting style of play, when shots are going in it makes for pleasant and exciting basketball to watch.
I see no need to extend the shot clock personally, the main reason is that some teams are already over possessing the ball and running too complex an offensive set while others have got it together batter and easily get a good shot off from their possession.
Efficiency needs to improve in the NBL, not sure that a longer shot clock will help, the other thing is defending for longer periods will increase fatigue, by the end of a game it could start to become less attractive to watch...
Last thing, how will a 30 second shot clock impact on overall length of games, it may not suit the TV time slot if we start to extend the games too long?!