Paul Murphy about Linux on mainframes

Paul Murphy wrote an extremly interesting article about Linux on Mainframes in his weblog. In my time at Sun i´ve heard several times from customers, that they think about it. Interestingly none of the customers really did it. Linux on Mainframe is purely an technology for sales reps to talk about with customers. You have a mainframe customer, that wants to save some money. Okay, sell him Linux on mainframes. After a while he will detect, that the performance is a little bit slow in relation to the big black monolith in your datacenter. Okay, sell him a pSeries or a xSeries with Linux or AIX. Two sales opportunities out of a legacy technology.
But to be honest, mostly the step in the middle is ommitted, because as wrote at the beginning: Every blue shop talk about it, none (or to be honest, there are a one or two, i was able to find, one in 2004) of them really done it.
Don´t take me wrong. It´s an interesting technology. But there is no technical rationale to do so, when you are not bound to the mainframe out of some technical reasons (mainframe backup for example). For big databases (SF6900 to SF25K-class, not the small sizes, that hobbists consider as big) you would not use Linux (you would use the absolute best available operating system available on the platform of you choice). For large consolidations of small servers i would use Solaris Containers or Linux on XEN on Opteron or a T2000. And so on … Okay, so where is the case of Linux on mainframes? Besides of some very special niches i´m not able to see one. And besides of this, the Paul Murphy collected some performance data, that casts some daylight on the performance claims made by IBM. (To be a little bit caustic: The last time i had to tune to get from 6 to 9 MBytes/s is some years ago. Nowadays the usual task is to tune FTP in the 50 to 60 MByte/s and above range.)
At the end, i want to cite from Pauls weblog:

Since both SPARC and x86 servers are considerably cheaper even than the p550Q, the question to ask isn't whether you can run Linux on the mainframe, but whether you can get the 92.5% discount you'll need from both IBM and Novell for this to make sense.