Well, 'beautiful' is to a certain extent a subjective quality. 'What makes a Mac Pro beautiful is X' can be interpreted as 'What makes a Mac Pro beautiful to me is X', and that's not really a statement that you can argue against.

But even so, the fallacies are either stretched or completely inapplicable. Both the 'no true scotsman' and 'special pleading' fallacies involve constantly shifting goalposts, but we've only ever seen Jormundir say that internal design is part of what makes the new Mac Pro beautiful. Where are the shifting goalposts?

Like, I don't think that the fact that it's not beautiful on the inside is relevant to the fact that it's a cool as hell mod; I think it's completely irrelevant. But throwing fallacies at the statement is just weird. I don't get how they apply at all.

Fallacies are irrelevant because there's no reasoning going on here -- the person you're responding to is making a subjective opinion statement, not a formal (or even informal) argument about aesthetics. Their statement doesn't even have a warrant or grounds, so to attack it with a fallacy is nonsensical.