I was surfing around YT and stumbled on this video last week, and the poster (a Chevy dealer), claims to have taken pics of the C8 mid engine rear quarter panels. I kept thinking it would be posted somewhere online by now since it was posted on 7/20/17, and maybe it has but I haven't read anything about it other than this YT video. Having said that, the pic quality isn't that great and for all I know they are C7 ZR1 quarter panels. The dealer also says the quarter panels will rise with the rear clamshell.
Fast forward to 8:30 mark to see the allegedly rear mid engine quarter panels.