I can't help but laugh when people talk about putting a Retina display on a desktop computer. The pixel count would be so high on a 30 inch Retina, it would probably crash the OS, and the GPU would need to pump out so many pixels, the performance would drop to unusable levels.
I am sure the technology will be available in a few years, not today.
PS. Your other ideas would add cost, however, I think they would work as an option.
Edited to say, I did not intend to dump on your ideas. They are all good. I just question the timing.
I don't think you should be laughing, retina is defined also by the distance of use of the screens, and an interesting article in macworld recently (can't find the link to it, I am sorry) explained that most of apple's portable line up is very close to retina already by virtue of the distance it's meant to be used at. The imacs are not too far off either. I don't remember the numbers but the high res 15" mbp would only need to increase marginally in resolution say by 25% to be labeled retina. Retina doesn't mean that the pixel density has to become equal to what the ipad and iphone has at 30", which you are right in assuming would cost a lot (ibm used to have one circa the early 2000s and it cost a LOT) and would require tremendous gpu power, because the imac's are not meant to be used at the same distance as the iphone and ipad.