But that's exactly it, right — everything you've listed are valid points in the design space, but they require a lot of coordination between various actors in t

But that's exactly it, right — everything you've listed are valid points in the design space, but they require a lot of coordination between various actors in the system. Process per test solves a whole swath of coordination issues. The post lists out what it would take to make most of nextest's feature set available in a shared-process model. There has been some interest in this, but it is a lot of work for things that come for free.