Yeah, I kind of feel like the hat block option is already going a little bit far in the opening dialogue (besides making it wider than it should be) - maybe it should be hidden under an arrow (alongside cap blocks, seeing as we're talking about syntactic sugar?) like the input dialogue.
Other block shapes should be unnecessary - if the block reports a list, maybe it should be in the list category, if it reports a sprite maybe it should be in sensing or control, etcetera. I kind of feel like Booleans aren't really necessary, exactly... except that their specific purpose is very important for new users to understand. Other block shapes will add confusion and complication - if you feel the need for a different shape, maybe you should just make a clearer block label/help text.
i've used this feature to recreate the when I am touching [ V]::events hat hacked block from scratch 3, as it would probably be useful for some projects
I was working on adding the background to custom hat c-slots in snapblocks, and I checked to see what they looked like in flat design, and, there's no outline showing that there's even a c-slot.