I think I understand your confusion now. There is also the image:icon:... -way of inserting icons. This is not a macro, so there is no naming conflict. Thinking about this again, I think this could indeed confuse users, though, if we have suddenly two ways of inserting icons where one of them doesn’t use the current icon theme even though it is promised to support them in the future.
Now the problem is that this image syntax expects that the result will be an image but our current icon theme uses an icon font instead of images. This affects all kinds of areas like the WYSIWYG editor but also the core rendering of images. I’m really not sure we can fix that without breaking things so I’m actually wondering if it wouldn’t be best to just deprecate that image-based icon syntax in favor of the new icon macro. Any opinions?