First, let's talk about the vision situation. How can you currently attain true sight of an enemy stealthed champion?
---Pink ward (only one per champion is available on the map at a time)
---Oracle's Lens (not available before level 9)
That's it. There's no other way. And pink wards, in addition to having the limitation of only one per champion at a time, also have the limitation of being visible. So whereas before, if Red Team had an Eve, and Blue Team put a pink ward, then either Eve could buy an Oracle to clear out the blue pink wards, or everyone on the red team could buy pinks of their own to clear out the blue pinks. The upshot of this was that, if Red Team wanted Eve to be able to gank, then they would have to invest in true sight as well. As it stands in preseason 4, Red Team can just clear out Blue Team's pinks without buying any true sight of their own.
This makes junglers like Shaco and Evelynn MUCH stronger than they used to be, because you can no longer cover a lane with pink to make it safe from ganks.
Now, it's true that Eve sits around a 50% winrate in soloq, but if we look at ranked 5s, she sits solidly above 50%, spiking up to above 60% sometimes. Her average winrate in ranked 5s over the past three weeks is about 54.4% (to arrive at that number I averaged the winrates available from lolking NOT taking into account the number of times that she was played per day, so this average is only an estimate). For contrast, only Sivir, Amumu, Ziggs, and Rammus sit at overall winrates higher than 54.4%. (source for all these numbers is lolking.)
|Evelynn popularity and winrate: Ranked 5v5, all levels of play. Source: lolking|
|Evelynn popularity and winrate: Ranked 5v5, diamond only. Source: lolking|
|Evelynn popularity and winrate: Ranked soloqueue, all levels of play. Source: lolking|
So now that we've established that there is something problematic about Eve, how do we fix it? Season 3 pink wards were obviously overpowered, and the rework to them in Season 4 feels great --- no more endless wars between the two supports in botlane for who will have pink-ward control over the tribush, the vision snowball that was possible in Season 3 now has significant counterplay that forces the winning team to act as soon as they've established vision instead of just waiting for a mistake and then winning the game, because their vision control won't last as soon as they clear out of an area.
However, what if there was a ward that revealed stealthed enemy champions but not stealthed enemy traps? I call it a "purple ward," and the way it works is that it upgrades your sight to truesight of enemy champions. So if Eve is standing stealthed in my vision radius, and the radius of my purple ward, then I can see her. But if she's standing only in radius of my purple ward, then I can't see her.
Here's a couple examples. Click on the image to enlarge it.
---A purple ward + a green ward = a season 3 pink ward except that it only sees stealthed champions
---Placing a purple ward in the middle of midlane allows you to see a stealthed Akali while she's in her shroud
---Because a purple ward is stealthed, it can be disabled (and then killed) by someone with a sweeping lens
---If a support places a purple ward in the side lane bush and stands in it, then he can see if an Evelynn or Shaco or other stealthed champ enters the bush. However, the instant he leaves the bush, he loses that vision unless there's a green ward also in the bush.
A purple ward would cost 50 gold and last for 3 minutes, stealthing itself after a brief period (the same as a green ward). Any champion can have up to 2 purple wards in their inventory at a time, and one placed on the map at a time. This way, buying a green ward and a purple ward costs the same as a season 3 pink ward did. A purple ward starts with 3hp but loses all but 1hp when it stealths. This way, it is still doable to kill both a green ward and a purple ward with a single sweep of a sweeping lens, but you cannot one-shot or even two-shot a purple ward before it stealths itself.
Why should purple wards be implemented?
---Allows truesight prior to level 9 without losing a "permanent" ward---at the moment, getting true sight of an enemy champion in a brawl forces you to lose a forward ward that you may have wanted to keep.
---Allows for counterplay to Evelynn with a much more reasonable counter-counter play: Evelynn's team either needs to invest in their own pink ward or a sweeping lens cooldown to kill a purple ward. This means that the presence of an Evelynn will require an investment by both teams, not just the team playing against the Eve.
What are some downsides of purple wards?
---Somewhat complicated to understand, because they require an interaction with another allied unit to function in a way not previously seen in League.
---Nerf some champions that are already relatively weak: Talon and Akali come to mind.
Overall, however, I believe that purple wards will add a lot more to the game than they will detract, and I think they're a very well-balanced solution to the current problem of stealth champions being overpowered.