Well, we've got plenty of statements implying he'll appear, and there's that silhouette that looks KINDA looks like him in the opening.
And wouldn't Ao rewriting time make time travel MORE plausable?
Also, isn't the show only supposed to be twenty-four episodes? if so, I'm expecting things to start heating up VERY fast. Also, I'm hoping we get back to whatever it is that Gazelle's group (I think) photographed in the basement a while back, because we've gone a while without finding out what E7 Ao's Lilith standin is. Although, in this last episode, Elena mentioned something about the thing in the basement, and did a pose that looked kinda like the thing in the blurry photo.
Also, I'm intrigued by the (presumably) Evangelion-referencing degradation of the next-episode preview...first, the episode would end with 'to be continued' and then we'd get credits, then the preview, which would always have voiceover...a few episodes, the voiceovers pretty much stopped, and I think this last episode ditched the 'to be continued', as well.
Also,
Christophe Blanc killing Truth...hell, that ENTIRE SEQUENCE, was just awesoem...we have Fleur taking Ao into the basement...then shooting Christophe, who turns out to be Truth, Truth just beats them down in a fraction of a second...and Christophe shows up with guards, has them distract Truth, gets the kids out, then calmly walks in and starts shooting at the unkillable Secret...and then kills him. Wow.
And,
did we get confirmation that Elena is Eureka's first child? She mentioned Eureka bringing her to Ao's world, and there have been several parts where Elena had flashbacks to Eureka's world...but Elena looks NOTHING like Eureka or Renton...