On some broadband dielectric coated galvo mirrors (well, most), polarization angle can be changed with angle of the galvo shaft, The traditional cure is overcoated aluminum reflective coatings on the galvo mirrors. There are tricks with left and right hand circular polarization that might help, but I have not tried that yet. Before anyone says. "how can that be?", the path length through the 16 or so dielectric coating layers changes with angle of incidence, thus changing phase of the light between the coatings.
You only have RGB, maybe RGBV in a modern low cost projector, but Chromadepth(tm) glasses do not depend on polarization.
The patent on using Chromadepth(TM) in laser shows has most likely expired.
A good pair of galvos has a small angle jump bandwidth of DC to 2000 Hz, maybe 2400 Hz. Large jumps have a much lower bandwidth. Keep you scan angle low and you can work magic. Widen it out and life gets interesting.
3D Laser faded out because the Chief engineer of a major laser show software producer is not a fan. HIs former partner, however, Was.
In the past some hardware outputted a dedicated Z signal that could allow you to generate X and X-Prime, for two scan heads. Anaglyph, Polarization, Active Polarization Rotation, field flipping with LCD glasses have all been done. When we use Ion lasers mixed gas or mixed pair, with PCAOM (our term for multi-line AOTF) we have eight or more colors for Chromadepth(tm), of which maybe 5 are far apart enough in wavelength to be significant (457, 488, 504,514,530, 568,647, 676)
A WARNING, higher power solid state laser projectors almost always use polarization cubes / waveplates for combining arrays of laser diodes for higher power. You have to know what your getting into if you buy a laser that does not use single mode diodes.
Single mode diodes for RGB at low powers are available from DTR Lasers for reasonable cost, but get glass collimation lenses to aid in maintaining polarization if you go that route.
Multimode high power diodes can have a low power side mode at a different polarization state that gets annoying.
A single mode RGB system of one polarization restricts you to smaller images at around 450 mW of available power. In other words, very small images in room light.
These challenges for a laser hobbyist, tough. These challenges for an Engineer willing to learn, not that bad. Some place I have some 3D images in Pangolin Format on an old hard drive from the planetarium days, I'll see if the drive is still valid.
Steve