I'm assuming since Quantal and Raring are so close to end-of-life (April 2014 and January 2014 respectively) that it is unlikely that anyone will upgrade from precise to these releases and thus loose this feature. If you are on this releases you can always compile the packages with this support yourself from lp:lightdm/1.4 and lp:lightdm/1.6.
I'm assuming since Quantal and Raring are so close to end-of-life (April 2014 and January 2014 respectively) that it is unlikely that anyone will upgrade from precise to these releases and thus loose this feature. If you are on this releases you can always compile the packages with this support yourself from lp:lightdm/1.4 and lp:lightdm/1.6.