I certainly don't know the specifics but there's a way that they can 'turn' 2-D movies into 3-D. They've been talking about doing 3-D versions of the Star Wars saga and James Cameron movies (Titanic, Terminator 2) for a couple of years too.
The 2-D to 3-D digital conversion was done for four sequences in "Superman Returns" and also for the climactic final scenes of "Harry Potter and the Order of the Phoenix". Looked pretty good too, although I can't begin to imagine how much work it would be to do an entire feature film.
Interesting idea, and a good excuse to see these films in a theater again, if true.
But if New Line needs some cash to help it through its current turmoil, why not just release the damn films on Blu Ray? I'm pining for these films in high-def.
I believe the main reason Hollywood is pushing 3D is to thwart camcorder-produced bootlegs sold in other parts of the world, but you're right, it might produce a new revenue stream for the home market.