This should bring the price way down, but rumour has it that a system will still cost US$3,500. Site information states that these are the hardware requirements of the computer (for a Mac):
Mac Systems
Apple Mac Pro with 1 available PCIe slot
System Software: Mac OS X 10.6.4
Total System RAM: 2GB minimum, more recommended
I would think that a bit more than any old Mac Pro with 2GB RAM would be needed to get the performance of the systems with additional cards. Also, there is no mention of latency. If Digidesign have done their homework and written the code to utilise Core Audio the way JACK does then there will not be any problem. Or have they stuck with the DAE? (horrors).
http://www.avid.com/US/products/Pro-Tools-HD-Native