Magician and switcheroo is good and all, but it's hardly good enough to justify filling an entire teamslot. Knock off, with it's new buff (making it the strongest reliable physical dark type move in the game in most cases) is far more usable, useful, reliable, and is able to work without having to sacrifice a teamslot. Standard choice tricking works the same as it always has, as well.
With Delphox's trick magician bit, you have to run switcheroo, plus I guess power-Herb and solarbeam is the consensus for the best move to work it with. So essentially, you're giving Delphox a support move that does nothing to recover or bolster delphox's defenses or otherwise help it survive, plus what is essentially a one PP move. Meaning that even more pokemon can switch in and destroy delphox then before, when it had the option of running even limited, weak coverage or boosting moves like CM.
And really, once the magician gimmick starts getting to be well known, as it's the only thing that makes Delphox stand out, good luck making it work. If you can get delphox to attack, steal an item, switch items onto another pokemon, and then switch items again (without dying, and considering delphox's bad defenses and typing), you were probably playing an opponent you could have beaten anyway without resorting to magician+trick.
Also, nearly every team runs a mega. All they have to do is switch in a mega and you've pretty much wasted a teamslot.