The relevant definition of prototype from Merriam-Webster:
"a first full-scale and usually functional form of a new type or design of a construction (such as an airplane) "
Remember, this design brings together a few technical components that have not been married together in this way in the past. So it will need to go through a certain amount of debugging and such. And of course it will most likely be used to complete the safety case for certification for operation at target speeds and to establish that it can meet the RFP requirements adequately too, before line production is started.
Don't know enough about the pros and cons of self steering trucks to make much of any intelligent statement except to observe the old dictum that was taught to us at Bell Labs over and over again: A component that is not in the system will never fail and will have zero maintenance cost, so think hard before adding a component about whether its addition is justified for fulfilling the requirements specified in the requirements spec.
Makes plenty of sense to me. I would imagine this is due to the heavy standards set by the FRA?
I think that one thing that should happen is that should it be set up as it would be in revenue service, is that Amtrak should put it on display at several key stations, DC, Philly, Boston, try to fit NYP in if possible. That way customers can provide feedback on what they would like to see changed or vise versa.