From my research it seems like not a good idea.
But some did it with no problems.
Although...honestly I think companies store their inventory this way.
One point was not to store it in a way where there's pressure on the keys. Another consideration was where the power supply or other heavy parts were - to store with those lowest to the ground.
There were a few ways people stored them - flat, on one end (lengthwise up), or on the "back" (widthwise up).
Lengthwise would be similar to how many people store guitars.
It would be convenient, but a Kronos seems more prone to damage than a guitar in this instance.

