I'd think.... zero. OS-X has six major flavors of the Bourne and Csh families of Unix shells already, any of which are at least as capable as Powershell:
% cat /etc/shells /bin/bash /bin/csh /bin/ksh /bin/sh /bin/tcsh /bin/zshPowershell is great on a Windows box, I agree. But only because COMMAND.COM and CMD.EXE were the only native alternatives until it appeared. Granted all shells have their strengths and weaknesses. But overall, Powershell is 20 years behind the times. They should have supplied that as a baseline part of Windows 3.1, and been expanding on it since.
By which I meant NT 3.1, the first release of NT. Not the DOS-based 3.1.