If the proposal includes hardware, does it include emulators (e.g. zPDT, Hercules), or is it restricted to 'real' hardware?
I don't think we should exclude emulators. Both the horrendously expensive zPDT and the free (as in beer and speech!) Hercules are valuable learning tools.
As for the actual hardware, it's OK to have Q&A about it, but the idea is to focus primarily on knowledge that's useful for current practitioners working on actual production hardware.
I would say "all of the above". There are, of course, existing forums for some of this. For example, there's a Yahoo Group for z1090, which is the zPDT/ID&T hardware keyfob - but it's where a lot of folks discuss both flavors of that emulator.
Inevitably Hercules comes up. Again, there's a group for it on Yahoo. Not sure if it suffers from any of the issues that brought on this proposal for StackExchange.
For practitioners, configuring LPARS or even ZDT instances requires an understanding of the hardware configuraiton, management, scalability and resiliency. Absolute +1 to hardware and software. For instance, I could think of some good questions about performance improvements and applications of SIMD instructions that could start a whole new thread.
So, what kind of discussion do we want??? Software??? Sure, preferably something about software that operates on the mainframe. since this is StackExchange, I'd think we'd be talking mostly about Linux on z, intercommunication between it and other software or operating systems. You know, cool stuff.
Something about how software interacts with hardware??? Yes. Enlightenment about how the hardware works might be helpful to answer a question about software that manipulates specific hardware.
How to make some program hardware-independent??? Sure. How to support new hardware??? Sure, we'll need that too. Maybe we substitute "hardware" with, say "operating platform"???
So...what don't we want??? I think that's the question here. Operating system bigotry??? No...no useless competitive debate. Here's what works for me and how??? Sure, just no "my USS is better than your Linux".