It doesn't work if you're going against GPUs. All the nice goodies we are accustomed to on large desktop x86 machines with gigantic caches and huge branch predictor area and OOO execution engines -- the features that yield the performance profile we expect -- simply do not translate or scale up to thousands of cores per die. To scale that up, you need to redesign the microarchitecture in a fundamental way to allow more compute-per-mm^2 of area, but at that point none of the original software will work in any meaningful capacity because the pipeline is so radically different, it might as well be a different architecture entirely. That means you might as well just write an entirely different software stack, too, and if you're rewriting the software, well, a different ISA is actually the easy part. And no, shoving sockets on the mobo does not change this; it doesn't matter if it's a single die or multi socket. The same dynamics apply.