What do you think about this design?
My ignorant take on the matter is that it'd be better for you guys to decide what sort of case you want to produce. Originally the C4 was a 9.85L chasis and now it sits between 11 & 11,3L and is apparently oriented towards custom loop builds, it seems a bit unclear to me what purpose your design wants to serve.
I like your idea of having no venting holes on the side panels and aiming to create a new cooling solution for the case. As I'm no expert on the matter, I trust what Josh says about AIOs here:
Ultimately, these forums might be a "small" (pun intended) representation of who you want your customer base to be. My personal selfish desire would be seeing a C4 with exceptional air-cooled thermals which could also accommodate AIO support as an extra, but that is only me and I understand I don't represent in any way the majority of your potential buyers. Best of lucks and keep it up, here's hoping the C4 will be a success.