Is there a reason why my 3d rendering program can render movies at 6000X4500 plus in video size?

Question

what hardware can support playing at that size, and project an image that size.

Answer 1

When mixing computer images with photo or film, the quality needs to be as high as possible.
35 mm film can be "burned" with images at the resolution you mentioned, with the results being good enough to project in a cinema. Admittedly, the equipment for printing to 35mm film isn't common- but it DOES exist.

Oh, and let's not forget the new "high definition" video projectors, starting to appear in cinemas.

Answer 2

theater quality video