I don't understand how this is an advantage. Yes, you can swap RAM with the system powered up, but what happens to the information in the module that was removed? Is the OS doing some kind of RAID-like memory allocation? The article wasn't clear on how this would actually work.
Servers have had memory mirroring as a feature for years. This seems like a cool extension of that technology. It would be an advantage in some systems where scaling out isn't an option and single node availability needs to be as high as possible.
Apparently, there's some coordination mechanism, where you tell the OS that you want to remove a certain memory stick, so it moves all the memory onto other RAM sticks (or uses paging to move it to your hard drive). Only then would you actually physically unplug the memory stick.
I remember the ‘good old days’ of Sun Fire 10k and similar servers. You could replace entire boards of CPU and RAM and the server would keep on trucking.