Hardware - best architecture to utilize current technological advances and may be possibilities in future. Modular bus, CPU as a card, memory as card, interface to connect existing cards and devices. At the top level it may be just a bus and bus manager. Possibility to interconnect buses. Like in C everything is a stream.
Software - super OS capable of creating environment to run other OS's, providing channels to use hardware simulating ports for current OS's, disk storage capable to simulate file systems used by current Os's and able to use such file systems independent of OS's.
BIOS - wakes up and creates inventory of devices (and interconnected buses), takes care of device changes and informs OS accordingly.
Super Computer - a computer which manages a cluster of computers. It has to be simple. Connect two buses, they start as peers. Over time one becomes master depending on uses - but not for the information. Connect an old computer - within couple of hours it takes over the old and shuts it down forever.