On the topic of Rengar...
How would you feel if he was balanced into a melee AD carry role?
How would you feel if he was balanced into a melee AD carry role?
He's already a melee carry. He builds AD and is a snowball champion that ideally should be able to carry hard. That's an AD carry.
I think the OP meant a fighter, and I think you know it :P
Actually, I think the OP is confused about what all those terms mean. Being a Fighter doesn't mean you can't also be an Assassin. And any champion with high base damages you build tanky is almost automatically going to become a bruiser.
Kha'zix is a great example. He has assassination potential (maybe not 100-0 instantly thanks to recent nerfs, though I do think he needed a love tap). He can also be played like a bruiser using his ult to navigate and survive in teamfights. He can also be built to be quite tanky with a Randuins and Banshee's in combination with his ultimate.
Something like the Fighter class is a little weird to talk about right now, because there seem to be two distinctive kinds of Fighters: "light" fighters like Yi, Yasuo, etc., and "heavy" fighters like Darius, Nasus, etc. I was mainly talking about moving Rengar closer to "light" fighter territory, the guys who are typically referred to as melee AD carries.
I agree that fighters are sort of awkward to discuss when it comes to League and it doesn't help that everyone has different opinions as to who is what and what a fighter is. Honestly, I don't think extended fighting like Yi and Yasuo fits with the Rengar feel. At least not in my opinion. To me Rengar is more about hunting. He should be stalking his prey and looking for opportunities to exploit weaknesses and then escape. That meshes more with assassin to me, and is the opposite of what I think of when I think fighter. Again though, just my opinion.