I don't know if it's trivial or if it depends on a lot of exo things but moving ExoIconChooser to libxfcegui4 could allow xfce4-panel to use it too for more consistency. What do you thing ?
It depends on several parts of libexo, most importantly the ExoIconView. Besides that moving it to libxfcegui4 would mean to add a libxfcegui4 dependency for Thunar, which should be avoided since libxfcegui4 is a very heavy dependency (in terms of size, relocations, ...) and libxfcegui4 should die in the near future. xfce4-panel (actually the launcher) can optionally depend on libexo to use ExoIconView, it could even run the icon chooser in a separate process so there's no hard-dependency.