Split brain issues are harder to solve, but of course there are protocols to deal with that too.
> And since CPU clock speed won't really be getting any faster, we have to scale out if we're going to scale at all.
What does CPU clock speed have to do with all this? It certainly doesn't affect communication latency and is a rather poor indicator of computing performance.
While clock speeds have stagnated, single core (thread) performance has been steadily increasing. Compilers are just not fully exploiting additional computing power yet.
Then there's always NUMA (non-unified memory access, multiple CPUs and memory subsystems networked together at hardware level) and in a larger scale, RDMA (remote DMA).
So my point was mostly that distributed applications are unavoidable because you just can't scale up past a certain point.