Forgot to mention that, at least for webkit, this is really a case for
slots usage as this is the same software, built for another toolkit.
This applies to a couple other ebuilds in this gtk2/gtk3 discussion, but
admittedly not all of them.

We have at least three cases that Alexandre summed up:
 * packages shipping gtk based libs only
 * packages shipping gtk based libs and other libs (gtk-vnc for example)
 * packages shipping gtk based libs and gtk or non-gtk utilities

Some packages most likely should be split, like avahi, but it is not
always in the interest of everyone as it makes things much harder to
maintain.

-- 
Gilles Dartiguelongue <eva@g.o>
Gentoo