To say nothing of the Power 7 795, which scales to 256 cores with 4-way SMT, for 1024 hardware threads.
http://www-03.ibm.com/systems/power/hardware/795/index.html
And AIX 7 will handle this in a single-system image:
http://www-03.ibm.com/systems/power/software/aix/v71/preview.html
Desktop operating systems, indeed.
Pfft. That site doesn't work with Firefox 3.6, only IE.
The System z hardware is no more EBCDIC than you are. z/Linux uses ASCII for messages, commands, and utilities, just as z/OS uses EBCDIC. The z/Linux choices include ports of RedHat and Suse. The port does not include translating these to EBCDIC.
Now, the old native Unix for z/OS, Unix System Services, *was* an EBCDIC Unix. Nothing ever said Unix had to be based on ASCII. Porting programs to USS was a challenge because too many programs made assumptions about the binary value of characters. Usually the fixes were simple, but sometimes the defects were hard to find. But if an assumption was made about the collating sequence, the problem was harder.
No amount of careful planning will ever replace dumb luck.