But the question is not if the icon is practical or silly, the question is if it makes sense as a Unicode character or should be handled at some other level like a GUI control or widget.
Should GUI icons, widgets and controls be covered by Unicode? That is a can of worms.
I understand the usefulness of the "external link" icon, but should it really be something you arbitrarily type into a text? Shouldn't it be part of the rendering of a link?