I finally found some time to work on this project. The first idea I had was abandoned. I am currently working on a case that combines a case with sandwich layout and a case with motherboard mounted on the front/back of the case. Since I went through four cases in under six years, I decided to make a case that I will be able to use in at least two different builds with two different layouts.
Internal volume has increased to around 18 l but this gives me even higher compatibility with components (especially with CPU air coolers).
Supported components:
Mini-ITX motherboard,
dual-slot GPU with length up to ~ 338 mm,
ATX PS/2, Flex ATX, SXF or TFX PSU,
tower CPU cooler up to ~ 182 mm tall,
up to 8 fans (92 mm),
water cooling: 2x 140mm radiator with length up to ~ 312mm.
Sandwich layout in three variants:
FRONT-LEFT VIEWPOINT



Variants of a layout with motherboard mounted on the front/back:
FRONT-LEFT VIEWPOINT



Hopefully, I will have a concept to show by the end of the month.