From my limited outsider perspective, it appears like there are way more CPU and FPGA startups than GPU startups - why is that when GPUs seemingly have lower barriers?
Most of the related startups are targeting the much higher-margin deep learning training accelerator portion of the GPU system market, and there are a lot there:
It's also a quite explored and already deeply optimized area.
Companies like TensTorrent, Graphcore and Lightmatter (for example) try to hit different spots of the architectural landscape (seemingly all optimising for 'cheap to tapeout' in all sorts of clever ways, but you still have to code for it (even though you often get python APIs and deep learning tensorflow/torch support, but that's probably not getting you to to max perf). Very interesting to watch, and hopefully one can get their hands on that kind of hardware and build a community around it.
https://www.ai-startups.org/top/hardware/