2D animation is not an artifact of the past, but it has been treated like one. It's an artform just like any other and its success depends on those involved with each project.
The Princess and the Frog was supposed to usher in a new demand for traditional animation. You can blame the marketing, the title or 2D animation, but the failure is one of story. It was poorly written! The animation was beautiful and the characters were interesting, but the movie was all over the place.
All 2D animation needs is a writer/director with something to say that speaks to moviegoers. Unfortunately we get rehashes of better films and self-indulgent movies that wouldn't pass a year-one film school critique.
I've never understood the failure of story because these films are made in slow motion. They take years! I was disappointed in FrankenWeenie, but I blame Tim Burton's lack of imagination and not stop-motion animation. The film would have been just as bad in CG.
I think traditional animation is fated for a comeback in popularity. It just needs quality writing and a good idea.