There are many potential designs for these things, but the first gen TPU is one that works, is in production, and has been described in a paper. But you have to differentiate if you mean an inference engine, or something that can also do training. For HoloLens, it's probably going to be an inference unit, which means it'll possibly look something like a TPU, perhaps with more specific hardware support optimized for convolutions (which are very important for visual processing DNNs these days), as the NVidia tensor units are.
There are many potential designs for these things, but the first gen TPU is one that works, is in production, and has been described in a paper. But you have to differentiate if you mean an inference engine, or something that can also do training. For HoloLens, it's probably going to be an inference unit, which means it'll possibly look something like a TPU, perhaps with more specific hardware support optimized for convolutions (which are very important for visual processing DNNs these days), as the NVidia tensor units are.