Obviously the manga is quite popular for Viz, and they have a tendency to snap up the anime versions of their manga properties.
But Full Moon wo Sagashite was always considered quite unlicenseable or unmarketable to western fans: magic girls, long running and hell to dub due to all of the songs (a very important part of the show).
We will see how it progresses, however Viz are noted for taking extensive liberties in translation and adaption.
But yeah, its a great series. This does bode a bit well for seeing Aka-chan to Boku (Baby and Me) as well, which was never fully fansubbed.