I've been spamming Evelynn Mid for the past 30 or so games, and I've climbed four divisions. She's a consistently powerful champion, and I'd argue that she's much better in mid or top than she is in the jungle. It's far easier for her to get gold for items she needs to make an impact when she's not completely dependant on ganks.
She's going to make a massive comeback soon - OP is right that she's sleeper OP. She's got a very powerful kit, even without the stealth -- you can build her AP or AD, tank or assassin. She fits every teamcomp and can be put in any lane. She also has high burst and sustained damage, and even has AOE and sustain in a teamfight by nearly doubling her HP from her shield.
Her stealth is probably going to go if she gets looked at by Riot again, because she still has a solid kit even without it. I've been an Eve main since beta through all of her iterations, and she's quite powerful right now, but tbh she's always been a strong champion, even after they gutted her and left her nerfed for a year.
It's all about the community perception of her - and times like right now when she's largely ignored is the time to really focus on playing and getting good with her. I've learned to use the community's silly mentality of only listening to what they do in LCS to my advantage because nothing I say or do will convince anyone that she's not garbage tier right now, much like it's impossible to convince anyone that LeBlanc isn't the most retardedly OP champion that has ever been in this game (lol), but I can guarantee that she will be complained about in a few months' time with zero changes to her kit.
When she does get picked in LCS though, she will appear in every single solo queue game until people cry and get her destroyed again for like the fifth time now. Then I have to go back to LeBlanc and be screamed at for playing her because I'm sure in a few months, LB will be garbage tier again to the community.