OP said DO DO! I think a c-pillar wall can look good and have a wow factor. You gotta remember to leave room for batteries and your amp/s.
Fuck seats..... (unless u have kids, then buy a second car)
I've realized my build will not be doable behind c-pillar. Back seat has to GTFO!
I don't have kids but I still transport friends and family. So I'm gonna get my wife a car and she can play taxi.