As another idea how about Optical interfaces for HDD's rather than the present SATA/IDE cable set up? A thin fibre optical cable from the HDD to a socket on the motherboard, would help with airflow through the chassis and more information and, at a faster rate, could be transmitted than the current technology allows.
Fibre Channel is widely used on servers. Boot the OS from SAS or SSD and all your main storage is on FC connected drives in another part of the room - or in another building. The main performance benefit of optical is distance, but electrical interfaces can be made faster than current SATA standards, so no need to replace internal SATA with optical interfaces. Having a tidy chassis is nice, but I tend to find that it is the SATA
power cables that are the messy ones, not the SATA data interface cables.
Fibre has it's own set of problems - special tools to terminate, minimum bending radius limitations.
What I'd like to see... a low power consumption ARM CPU based motherboard. Sort of like a
Raspberry Pi on steroids. But perhaps supporting the ARMv7 / hard floating point chips. Unlike the Raspberry Pi, the board should expandable to add memory and various storage/interface devices. Apart from the people that want to run some Linux distribution or Android, there is the HTPC market wanting a small, low power, fanless device.