It should be noted that I believe you can get access to Linux s390x boxes in the cloud for not very much money.
It's the z/OS side of things that tends to be prohibitively expensive. Thats almost entirely due to software licensing and not hardware though. The hardware is really not much worse than POWER or any other non-x86 specialty hardware.
So if you are making a product that could be big in the kinds of places that have a lot of mainframes, and you are offering an on-premises version, I'd say to go ahead and get a port to s390x tested (on Linux). It's very cheap to do and a potential selling point for a lot of large companies. Then from s390x to z/OS Unix it isn't all that much more work if you decide to take it all the way and offer official support, i.e. if somebody is going to sign a big contract where mainframe integration would be the differentiator between you and a competing product. Once you've got commitment for a contract of some kind I'm sure there are ways to get the access you would need to test under the expensive software.
> I believe you can get access to Linux s390x boxes in the cloud for not very much money.
Could you say where and what "not very much money" is? Like, are we talking $5 DO droplet equivalent or only a few hundred bucks a month? (but to be clear, this is a serious question; I'm a sucker for weird options and would be interested in running a s390x Linux box if it doesn't have too bad price+caveats)
Go to https://cloud.ibm.com/vpc-ext/provision/vs and choose North America > Washington DC > Washington DC 2. Click "Change image" and choose "IBM Z, LinuxONE", then pick Ubuntu. I get $0.09/hour for 1 vCPU/4GB RAM with storage extra.
For fun, then try picking z/OS instead of Linux and see what that software license costs ($/hour). Take a guess first how much you think it'll be and then see if you're right.
It's the z/OS side of things that tends to be prohibitively expensive. Thats almost entirely due to software licensing and not hardware though. The hardware is really not much worse than POWER or any other non-x86 specialty hardware.
So if you are making a product that could be big in the kinds of places that have a lot of mainframes, and you are offering an on-premises version, I'd say to go ahead and get a port to s390x tested (on Linux). It's very cheap to do and a potential selling point for a lot of large companies. Then from s390x to z/OS Unix it isn't all that much more work if you decide to take it all the way and offer official support, i.e. if somebody is going to sign a big contract where mainframe integration would be the differentiator between you and a competing product. Once you've got commitment for a contract of some kind I'm sure there are ways to get the access you would need to test under the expensive software.