Dynamic pricing makes some sense in the concept of trying to capture maximum demand, it just feels horrible as a customer.
1- I'll make a scene
2- I'll never come back
3- It is probably a discrimination lawsuit waiting to happen
Again, not saying the outcome is different, but socially it won't be accepted, as it removes that veil.
If you have a defense (or a response where the phrase "in practice" appears anywhere, really), then that's a separate matter, but it does not follow strictly from the matters presented that the coffee shop "will have to raise prices" in order to pay their employees more. That's, in fact, a stronger claim than the factorable defense that the author (and others who make the same argument) is depending on.
In other words, both "have to" and "can't" are doing a lot of heavy lifting.