I have designed a single-fan PC case
Somebody, please implement it! 
Its features:
- 1 fan only (be about 18dBA or less, vibrationless-mounted, insulated)
- powerful (can hold 5 of the biggest expansion cards, 6 big (noiseblocker-encapsulated) HDD/ODD drives (3 of them exposed))
- compact (52 × 32 × 16 cm)
- (simple) straight airflow (one main circuit-flow, one intake point on the one end, one exhaust point at the opposite end)
Apologization: I am not a case-designer at all, just a (dissatisfied) user.