I really like the concept, but the thing that's making me balk now is using the terminology "spoiler" for a property that could and very immediately would be used for serious things like trigger warnings and hiding the sort of stuff that you can't unsee, and fun but not spoilerish things like games, or huge/pagebreaking images, or even tl;dr out of courtesy for a friend who you know is reading from their phone.

If this happens, and I hope it does, I would want it to be called something that is very clear about the effects of the feature, and then leave the suggestions on use (spoilers, trigger warnings, etc.) for a FAQ.

I'd also like a nice large "expand all concealed items" or some such toggle, as a very easy way for someone who wants to view everything to not have to deal with, say, 25 concealment tags which were someone's idea of being cute.

Having it be textually and visually distinct from the standard cut-tag could be useful as well.