So, you may have noticed a 3D trend in film lately. There becomes a question of permanence. Is 3D here to stay? It seems like a fad. After all, 3D was a gimmick in the 1970s and 1980s, and even back in the 1950s.
However, 3D has something in common with synchronized sound (a property of films known as "talkies") and color. It's part of how we experience reality. Reality has sound (except to the deaf), reality has color (except to the colorblind, though even they can see some colors), and reality is 3D (except to those who lack depth perception). So, while I'd say that films don't need to be in 3D, they also don't need to be in color. It doesn't mean that the technology will go away.
That being said, the previous point that 3D has come and gone might indicate that it will fade again since the technology wasn't accepted just because it was widely available.
Personally, I think that 3D will first solidify itself outside of theaters, where individual people watching their films on personal laptops or handheld devices will allow for the use of autostereoscopy, such as via a parallax barrier. That is, you'll no longer have to wear fancy headgear for 3D, since the screen will effectively "know" where your head is, since you won't be likely to change it, a la how the Nintendo 3DS will work. (It loses the 3D effect if you're viewing the screen from off to the side.)