Rengar is good but his ultimate is god awful. It's so pointless when you compare him to Khazix. Khazix can EASILY get away but with Rengar, once you're in, YOU'RE IN, there's no getting out. His ultimate is so garbage and losing the ability to surprise your opponent just makes him even more worthless. I'm guessing something like a TF ult, which makes it alright to an extent, but in reality, it's going to hurt Rengar even more.
I think he said the idea is to make it purely an auditory cue. Like you hear a sound if you're in Rengar's vision range.
I'd take that in exchange for quicker stealthing. And the pounce effect is still in I'm pretty sure. They just wanted to remove his ability to pounce from seemingly nowhere, which will be changed by make you aware through sound that he just ulted.