1. Chevron and DY: If a dishwasher at least arguably cannot become treif, then how exactly would one utensil within a dishwasher make another one treif? Is the entire dishwasher filled up with water at the same time? Are we assuming that if some amount of treif food was stuck to the pan and went into the dishwasher and during the wash cycle that food touched a coffee pot within the swirl of soapy water, that the pot would then be treif? I mean, maybe. But I can’t imagine that if it happened in your kitchen sink, your rov would say it’s treif. Why should it be different if it happens in Starbucks?
2. That is not how halachic suspicion works. If someone knows someone who switched the milk in a specific case, that does not mean that there is a halachic chashash that the milk was switched in other cases.
2a. I don’t believe that there’s a substantive difference between keeping Cholov Yisroel as a din or as a chumra. Since nobody can claim that it has the status of treif al pi halacha, it becomes a matter of what words you use to refer to it, but the milk is the same.
And the reason that they wouldn’t is exactly this; they have a hashgacha that they presumably pay significant amounts of money to, so they obviously want to get frum customers. They wouldn’t switch the milk because if customers find out and tell the rav hamachshir, they will lose their hashgacha and not be able to cater to the frum community. (In the case of a convenience store who happens to carry cholov yisroel milk, I miiiiight think that it’s at least worth a case by case examination.)