Wait, do people actually toss out their old Macs instead of reselling them or gifting them to family members? I've seen lots of people make reference to "throwing out" the monitor with the iMac, but when you're reselling it or keeping it around as a secondary machine it's not really an issue (though in the case of the 5K iMac it's certainly pricey to get an external monitor that's as nice).
Just FYI Luna Display only supports 5K resolutions at a maximum of 45 Hz, which might not be ideal for video and motion graphics work.