Re: "Whew, wondered where we'd put those 200,000 BTC!"

If you focus on user-experience, simplicity, and minimal dependencies you might end up writing an exchange in python and running it on this: http://micropython.org/ , and then getting an insurance company to underwrite customers for any loss, including hacks.

Next step is make it run on a cpu you can audit the VHDL for... http://yasep.org/

I appreciate your ideas, how much would they scale? Can one squeeze 300 customers per unit and link many parallel units?