Since I have never used a grappling hook before, even I do not know how it functions. However, from what I can tell, it seems that all you can do is teleport to the block in which you are looking at (Please correct me if I am wrong).
However, I feel that the command that L_E_ is proposing is different. He says that this command should teleport an individual to the next clear space directly above them, even if they are not able to look at the area in which they want to go to. I personally agree with this idea, as it would assist in getting out of enclosed spaces underground. However, instead of making it a donor perk, I think it should be available to any player regardless of any rank, but have a fee and cooldown timer upon using it, to avoid overuse/abuse. I do not believe this would go against the EULA since everyone would have access to it, without an advantage.
TL;DR - +1, add a fee and make it available to everyone
