Hmmm... There were a couple of instances, but the ones I remember semi-clearly were Rei's shouting face showing in the scenes where you first discover the underground facilities and Nidhogg's face near the end of the Drakan route. I think Lisha also had some moments but can't remember where in her route.
As for the ideas in the Steam discussion, I'm basically with everyone else in that Drakan and Lisha are the most viable options for any extension. This makes it even harder for a Tix route to show though because the Hunt route would have to be the canon one. Unless Sable was passing through pixie territory during a Hunt, having them meet is kinda hard and exactly the type of oh-so-convenient situation that I dislike. (Not hate per se, I wouldn't be too against it, but... yeah). As for Rei, I see no possible future. At all. Eth is almost as bad, but isn't a hopeless cause, but I don't see any action situations happening there. Sad because they made me laugh the most, but at least I still get to see them in the second year right? Right? Jorou... nah. That's gonna have to happen waaayyyyy past Sable's second year at Amadronia so she's not plausible either. Wow it's so hard to type this almost spoiler-free.
I also agree with waiting a year to see what happens first, but if/when you DO end up crowdfunding, I'll back it immediately. Assuming I get notified about it somehow lol. Best of luck to ya Zetsubou.