How do you justify the fact that only some of the students get the pleasure of an in-person grilling? Or, am I completely misunderstanding the process you're going to be using?
In my plan, each student is interviewed at least once. Ideally more than once by the same teacher, so the teacher can get to know them a little better, spot areas where the student needs more help, etc.
There's still a scaling problem, but I think it makes the ~200 student classes we have now more feasible than 100% autograding. I also like the other commenter's suggestion of coming back to interview certain students each time, if they need it.
Is this about pleasure or about measuring knowledge?
A lot of stuff you learn and the way you learn it isn't necessarily pleasant, but frequently you still have to do it and you really discover 20 years later why it was needed.
No, it's about why only a subset of students get singled out for extra scrutiny, literally arbitrarily, as the selection procedure itself is defined as "random sampling."
random sampling is an effective method for inferring the same information about the larger population that is being measured in the smaller sample, to a certain degree of confidence based on the sample size and known distribution of what is being measured. These concepts are fundamental to statistics.