I'd like to see Johnny Thunder's Adventures revived at some point; there's a lot of creative potential, and it would be cool to see some familiar faces in Lego narratives again. It'd be really neat to see what they could come up with for worldly structures in light of how awesome some of the Ninjago temple builds are.
Imagine how cool something like this would look using modern building techniques and parts
Yes, imagine if they introduced different races of aliens? They could've used it as a launching point for reviving the expansive Lego Space universe... But uh, evidently it didn't sell well enough to constitute that kind of attention.
As far as discontinuing goes, I'm thinking they should probably cut off The Angry Birds Movie set line.