That's not shifting goalposts, that's the goal from the start.

You seem to be throwing a lot of technical terms. Could you elaborate on where exactly do you see overhead coming from in a multiprocess vs. multithread architecture? And which data structures can be shared between threads but not between processes?

Scheduling overhead is identical and pure OS memory overhead is slightly higher for processes (they need more "accounting" data), but everything else can be optimized at the application level. Furthermore, shared memory lets you share data structures between processes just fine (heck, some data can be shared between processes and the kernel!), and since I assume the content processes will be dynamically linked, you're not even going to load shared libraries multiple times.