This is now five years old, and while obviously the premise is more correct than ever (computers don't look much like a PDP-11 architecturally), the conclusion

This is now five years old, and while obviously the premise is more correct than ever (computers don't look much like a PDP-11 architecturally), the conclusion ("imagining a non-C processor") seems less strong. We are seeing (and were seeing, even in 2018) a strong separation between linear and highly-parallel code, most obviously in the rise of Python for machine learning and scientific computing. It is still very convenient, when performance isn't paramount, to write in a single-threaded style and to a flat memory model. When performance is important, it's then appropriate to switch to a language better suited to parallel programming -- one of the computational-graph languages in something like Pytorch, some other set of primitives on top of CUDA, or even something more experimental like Futhark. Performance-critical code has always had its domain-specific languages, and they seem to be becoming more common, not less, and the hardware is being built to match -- as the CPU+GPU combination common to desktop PCs, as vector extensions to x86 (which have their own primitives making, essentially, a DSL of their own), or things like the M1, which bolt a GPU to a CPU to give both high-speed access to the same system memory. In other words, perhaps what's really out of date is not C, but the concept of a general-purpose language which is equally well-suited to any type of task.