Already mentioned up thread — Distributed Smalltalk.
"Open a debugger where you can trace the full stack on all involved machines."
"Inspect objects in the debugger or open inspectors on any of the objects, regardless of the system they are running on."
April 1995 Hewlett Packard Journal, Figure 7 page 90
No, that would not be enough to make anything work. What I can think of is an IDE that had access to all the VMs running and some plumbing for the VMs to communicate. I would love to be able to spin-up Smalltalk VMs so I can simulate a full system on my desk. Having separate IDEs running means I don't have any integration so I have to debug in multiple different IDEs when tracing communications. I can imagine some of the debugging and code inspection that could be extended to look at code running simultaneously in multiple VMs.