I'm hardly an engineer and probably would not take the time to test out my concept, but it seemed like a good idea, so I'll throw it out here. Hopefully, this is a good place to discuss such and idea.
I'm thinking it would be possible to design a passive, and active, 3D system for a projector by using something akin to the color wheel of a DLP projector, but instead of colors being on the wheel, the polarizers normally used in passive systems would be on either side. That is, one half of the circle would have a polarizer for one eye, and the other side the other polarizer. The wheel would then be synced with the refresh rate of the projector to show every other frame in one polarization, and the other corresponding frames in the other polarization. With 3D content designed for active shutter-based systems, that showing frames alternatively for each eye, the content may be instead seen with regular polarized glasses by each eye seeing every other frame, as is done with active shutter glasses, by each eye's polarizer blocking every other frame's light.
This seemed like an interesting idea for an alternative to the expensive active shutter solutions we have, which require hundreds of dollars to be spent on glasses. It would only require the purchase of one device to make the same concept apply, while leaving the cost of the glasses insignificant.