Oh it’s very much a quagmire, though it can be a fun one. Yup, glad you see it that way, I’m not challenging what you’re partial to either, in case that wasn’t clear. Interpretation is a very individual thing after all.
I would say that even if it could be interpreted as demanding, the intentions behind the question could be anything from malice to distress. As for choice, it would add pressure to the question but I don’t really see the choice changing from if the question was asked with a lower tone. For instance, even a low voice could be menacing depending on tone. Regardless of tone, the person being asked still has the choice of answering, lying, stalling, not responding etc. Though obviously the attitude of the person being asked could change and thus they might go with something they wouldn’t have chosen had they been asked in a different manner.
As for the example in your second post, what you’re doing is technically adding variables to the mix. You have identified the hypothetical asker to be the boss of the person being asked, which obviously adds the whole previously existing relationship into the mix. Not to mention there’s the personality of the person being asked to consider, but all that’s more on the motivational side other than that of grammar, I think you would agree.
That being said; “Pass me the tea-kettle would you.” Is indeed some sort of neutral question/demand/request that politeness/cultural pressure dictates that we follow without much of a choice, although we could perhaps pretend we didn’t hear. Or fling our feces at them. So the choice is still technically there. Not to mention it would change the narrative dramatically, as is the case with punctuation.
But I don’t really feel that there are any hard rules on the matter other than the obvious ones, so agree to disagree on that. I wouldn’t think less of an author for using caps (if it was justified given the situation), the primary thing that would affect me and my reading is the flow of the sentences.