I emailed TD about this a while ago and his reply was that when demand was high enough he'd release an Android version.
So I suspect that within the next 6 months we'll see SD for Android released
Keep pestering him and he'll soon realise that demand is high enough! As Peter said, he was not going to release it for Apple products due to a number of problems with them but we saw how quickly he changed his mind.
SD is absolutely the best product out there for VFR GA. It also helps that Tim is a pilot himself, an obviously brilliant software developer, and listens to pilots, and has kept the price sensible. I just hope the likes of Jeppesen don't make him an offer he can't refuse...