I'm not really against graphical smilies at the client level, but wonder what the benefit is...

If mIRC ships with it enabled (being the most popular IRC client) users will think everyone in the world sees their strings of cute jumpy little smileys as they do. If it ships with the feature turned off, users who want graphical smileys would still be posting to this board asking for the feature.

It adds more bloat to the download and would probably slow down scrolling (scrollback).

I'd venture to guess that their would be other needless problems associated with it... the fixed size of the gif and the different font types/sizes would make for good uneven line spacing and chunky scrolling (unless the screen is rendered which would mean more bloat and slowdown). If smiley patterns are replaced with images to help speed up scrollback, then you have issues like what happens when the buffer is saved or what goes in to the clipboard for a copy-n-paste.

It'd be interesting to see how that all gets sorted out.