My joke fantasy startup is a cloud provider called one.computer where you just have a slider for the number of cores on your single instance, and it gives you a standard linux system that appears to have 10k cores. Most multithreaded software would absolutely trash the cache-coherency protocols and have poor performance, but it might be useful to easily turn embarrassingly parallel threaded map-reduces into multi-machine ones.

It's relatively easy to have it work slowly (reducing clocks to have a period higher than max latency), but becomes very hard to do at higher freqs.

Beowulf clusters can get you there to some extent, although you can always do better with specialized hardware and software (by then you're building a supercomputer...)