We NEED an item that gives refillable pink wards

Say the enemy Rengar has 25 kills. You're at 45 minutes, eveyone on your team has full build.

How do you prevent Rengar from killing your ADC? Once you see the exclamation mark over someone's head, place a pink ward so you can see him and CC him to the other side of the rift. However, everyone has a full build. No one has room for pink wards. Pink trinket is removed. Red trinket does not reveal units. Is it REALLY Riot's intention to not have a way to counter stealth champions in the later stages of the game? Oracle Alteration "reveals" them, but does not seem to make them targetable, which really defeats the purpose of using it. Then you will know where he is, but you still can't stop him, because he will pop ghostblade and have 900k movement speed anyway, so you can't even just run away. Plus, the detection range is barely larger than his jump range anyway. At least with pink wards you can use the information you get from seeing which of your teammates have the exclamation mark to place the ward close to him.

One could argue that Rengar shouldn't have 25 kills in the first place, but sadly a lot of people do not respect his gank pressure and feed him, so that is not really relevant.

I said years ago, probably back in S2, that there should be a special slot for wards. Of course, this was before Sightstone, which alleviates the need for that somewhat, but not completely, as buying Sightstone on Kalista is on par with getting Runaan's Hurricane on Blitzcrank. This is now even more true than it was in Season 5. At least when we had pink trinket you could choose to buy that if you needed to counter stealth champions.

Also, yes, most games don't go to full build, but some do. I just had one go to 57 minutes because Rengar was the only fed person on the enemy team, but we could not counter him effectively as everyone had full build and I (Thresh) sacrificed a build slot in order to carry a pink 24/7. I also had money for full build since like 35 minutes; I was quite fed since my ADC and I did exceptionally well in our lane. That sacrifice of a build slot led to less armor/fewer ways to protect my team from Rengar. I can say quite confidently that if pink trinket was still in the game, or there was another way to get pink wards without sacrificing an item slot, we would have won that game.

That said, I do not consider Rengar OP. It's just annoying to have people feeding him and then having no way of turning the game in your favour.