True, but on Windows the approach is then to use COM servers, which have a faster IPC model, and can even serve multiple clients, depending on how the appartement space is configured.
"Faster IPC model" than what? Faster than writing to and reading from a pipe? Faster than POSIX shared memory?
If you want the isolation features of a separate process, you can’t substitute it with a single multithreaded COM server process.
.NET tried this with app domains, which are now deprecated.