Maybe on some other forum or something, but certaintly not here, because there isn't even a scene that would even suggest that.
And how is it "everybody"?
I don't expect Connie to turn out a titanshifter, nor did I expect the random Scouts.
Do I think Sasha is one? No
Do I suspect some of the main characters? Yeah, I do.
Rainer has so much screentime, he has probably more minutes than Mikasa right now, to the point where people started to mention it when he didn't appear for 2 episodes.
Ymir and Christa weren't exactly random noise in the background. Something was bound to happen with these two, at least Ymir was already a "get's eaten soon" candidate for me.
On top of that, we have seen 3 Titanshifters right now. The beast Titan is most likely one too and so are the Colossal titan and Armored Titan. Considering that Eren's father injected something into Eren and Eren is the only Titanshifter out of the "main-crew" we can expect something like a virus, or gene modification etc.
Now after what happened in Connie's town, we can be even more sure that Titans might've been humans once. That means, even if only 1 out of 1000 "injections" (or whatever that beast titan did) becomes a Shifter, we might see a few more comming up.
And then there is Annie's training scene with her father, where he sent her off and said to her that it's okay to "hate the world and make everyone your enemy". Annie turned out to be a titan on a mission inside the walls. Guess her father knew about her condition? Did he send her? Did someone else send her?
So what if that guy who sent Annie, send another 20 or so to spy and do stuff.
Well, I don't know, I think it's part of the story and part of the build up we've been given so far.
edit: talking about Ymir, didn't that talking titan (the one in season 1) call a human "Ymir's People"?