Excellent point about getting all the connectors onto a common panel side wall. The same would apply to any daughter boards that one designed.
The downside is the cost, physical size and quality of the cables to do the linking.
So, maybe panel mounted sockets with pre-soldered linking cables for the commonly used ports:
USB x 2
would be enough. I understand that HDMI is fussy about quality though - nasty RF problems can result from bad connections. (I don't know what I am talking about, but that's what I have read.)
Maybe even a PCB mounted to a sidewall to use PCB sockets?
I will fire up the CAD and knock up a side wall for the PiHouse (http://www.thepishop.org/cases.htm
). Also time to dig around for some suitable panel sockets.
The real problem is that the darn plugs stick out such a long way before you could bend a cable round to fit to a side panel wall. The size of the overall package starts to get big - which somewhat defeats the idea of having a "Pi in the pocket" or in the school bag - there are mini-ITX gadgets which would be smaller <g>
One good thing, a wireless keyboard/mouse adapter only takes up a tiny space sticking out of the USB port. Ethernet is a lump - at least 50mm to bend the cable. Maybe a tiny WiFi dongle would be better.
Power is a pain if trying to bring it out to a side panel.
I think it highly unlikely but does anyone know if the RPi can be powered from the 5V GPIO line? If so, bringing out a power connector would be simple.
There are some very short cables that might do the job: http://tinyurl.com/d48k49c
Life's single regret: not patenting dongles when we invented and named them to protect the Wordcraft word processor on the Commodore PET!
You can buy 31 RPi3s for the £639 price of one Samsung Galaxy S7 Edge smart phone - who buys this stuff?