Recently I have been fortunate to do some architecture work for putting a Linux capability on System z, specifically z/VM.
One of the things that has struck me is what a truly strange beast this Linux on z really is.
First of all, if you look at the way regular linux is developed, there is a comminity around a number of upstream projects, that a distro like Fedora or Debian take and release. Then for enteprise market you have companies like Red Hat who come along take a Fedora release and polish that into RHEL.
Where is the Fedora for System z?
One the benefits of Linux that are sold to the enteprise is that there is this vendor agnostic community behind it all.
Then you have to think, what will you run on Linux z? I have an application say written by a company in something cross platform like J2EE, ask the vendor if they will be able to support it on Linux on z, I think there will be few who would.
The only stuff I have seen running on Linux on z, is either homegrown (and so home supported) or from IBM, who have a vested interest in selling the hardware. I know Linux on z offers great consolidation oppotunities, and the eco credentials are great, but what are you going to run on it???