I think your right. I also think it will be a very stylised fight, using creative effects and angles. I think that type of censorship works so well for Hisoka as he is a magician, it's like you are trying to keep up with his tricks (see Hisoka vs. Togari in Trick Tower).
The 1999 series actually DOES show Hisoka's arm being dismembered.
Though it does it in a weird spin way that zooms in on part of the arm
and rotates the arm around until it is dismembered. Though it's zoomed
so you can't see the break but from the angle of the arm it's obviously broken.
The manga actually never shows Kastro "ripping" off the arm.
Rather he does his tiger bite fist and the arm is suddenly
up in the air and dismembered. Obviously from the tearing
on the arm it was clearly torn off. But you never see the
arm actually being ripped off. I mean you never see anything
like this
https://www.youtube.com/watch?v=2L-Z9OJaIPQ&feature=related
Instead you see this
Notice how you only really see the result but never the process?
My guess for how it will look...
Kastro will have his hands positioned in Tiger Bite Fist towards Hisoka's arm.
Hisoka will still have his arm attached. Kastro's hands will then switch positions
so that they go through Hisoka's arm (causing it to dismember) this part will
be shown using the quick animation (like with Hanzo's quick chop). It will
look like Hisoka's arm just popped off which is the same effect as the manga.
They can even use nen to their advantage to censor. They would just have
the nen block the view of where the arm breaks. In a way the DBZ clip
did this too except with Piccolo's blood. With an actual arm being ripped
off you would see a lot of blood for sure but also the bone and nerve endings
and what not. In short it would be very disgusting. Togashi shows it actually
rather classy. Something you would expect from a guy like Kastro.
Now what probably WILL be censored.
Hisoka will still pull the card out of his arm but you won't see as much blood.
