I am a fan of creating your own standard and ensuring that these are consistent within your product. To me, that is what makes your product look professional and provides that quality user experience.
As you pretty much pointed out throughout your great article, capitalization rules could depend on your target audience. All caps? It works for Giphy but it won’t work — excessively — in another environment that deals with a lot of text. It could work, however, in that “a lot of text” environment in places to showcase a visual hierarchy where it may be a label within a page.
So it’s never good to rule anything out. I once had to intervene between a visual designer and an editor, where the visual designer wanted “small caps” in a UI and the editor, who was vehemently against all caps. :)
Capitalization is a touchy subject for some of us.