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It is already available, https://www.ibm.com/products/z-and-cloud-modernization-stack

You mean timesharing? :-)

I suspect that for most organizations that use mainframes today, there are so many integration points and so much data is involved that the economics that drove a lot of early-on timesharing no longer apply.

It's one of the major ways to get a mainframe these days, even companies you'd expect to have one on premises might actually have a lease on one running in IBM datacenter with VPN to internal network.