Shaco main here. I've got 250 games as shaco this season. I have probably over 150 games as AP shaco, and happen to love boxing.
Boxes are completely AP based.
Riot cited that this nerf will tone down shaco's early jungle clear, but in reality it is a MUCH bigger nerf than that.
The last nerf was especially huge, and hits AP shaco harder than AD shaco, which I find odd since I think AD shaco is all around more powerful. Even if you max ap, you will never come close to killing someone as quickly as if you built ad, and boxes were exactly what filled the gap between them.
If you build ad, your boxes will now never go beyond 40 seconds, and if you build ap, it will gradually go up. But now, even if I build AP, the boxes rarely become worth plotting with until the very end game when it goes beyond a minute again, assuming you have probably at least 500ap, and even then it's simplly not a huge force to be reckoned with. Nearly gone is the objective control with boxes at baron/dragon, instead you have a rather flakey clown who everyone knows is at the objective and is easily smashed.
Regarding combo-cluster boxes, you now have only 40 seconds to make your entire cluster of boxes, where your opponent basically needs to trigger it immediately before they begin disappearing.
Warding for your team using boxes is now much shorter lived.
I also thought AP shaco was a viable support, (and passable top/mid to throw them off) until this update. AP shaco support has a risky early lane (lvl 1-4) with little to offer, but much to offer later.
What I think would have been more logical is if ad shaco was balanced down more, rather than completely crushing ap shaco.
All in all, I think 40 second boxes are simply too short. I really miss the 60 second boxes, and I miss how they could become tantamount if you scale into late game without your early jungle being denied. It was the most powerful thing about late-game ap shaco, but now late game AD shaco is simply totally superior.
I miss the ability to plot box clusters, something which has been tremendously nerfed.
Boxes were what made late game ap shaco powerful, but now a huge chunk of that is gone, bringing even an AP shaco main like me to begin opting for AD shaco unless they pick a heavy armor team.
I feel as if a major core of who shaco is has been taken away, rather than an overpowered edge that needs to be toned down.