Are you saying Toyota has customers walking along the assembly line as their vehicle is being assembled? If not, then I don’t see what your first sentence has to do with your last one. Again, I do not see how the manufacturing assembly line analogy fits with effective customer review of what is being created for them. I can agree that the creators/producers of something could have continuous review of their work as that is exactly what an agile team can be doing. And early agile ideas (e.g., XP) advocated having a customer (representative) working with the team day after day. But, even then, there was an end of iteration review for more people from the customer to see what had been done that iteration since not all of them were expected to be there day after day. In fact, the latter could produce chaos if all of them did not agree on the same vision and details for the work.