The narrow tunnel-gage of Boring Company is designed for cars... presumably it'd be possible to have a train vehicle with a form-factor more like stretch minivan than a bus. Lots of moving parts because many many more doors to open-close than a traditional bus or subway. But still, if stop-to-stop times are under half an hour, is it okay to seal someone in stretch-minivan-like train car without a bathroom for half an hour? I dunno.

It does mean that non-stop from LA to San Jose would be right out though. Being conservative and assuming a 300km/h vehicle, you'd want at least 3 stops along the way if people are completely trapped in the vehicle without even being able to stand up, much less relieve themselves.