Ah, nice idea, except that it means you need to disable the automatic fill, re-enabling it while you use the toilet so that it will be full enough to flush properly when you're done.
But it seems to me that it *does* mean that the cistern is remote from the pan, i.e. not close-coupled. If the cistern is below the basin, the cistern can't also be above the pan, can it, otherwise the pan would be in the way when using the basin.
Also it strikes me there could be a problem of there not being enough height for the bottom of the basin to be higher than the "full" mark on the cistern while still having enough head of water in the cistern to give a decent flush. Do they mount their basin higher up? With steps leading up? Or do you stand on the toilet to use the basin?
But yes, de-coupling the cistern from the pan does save a bit of floor area - it means the pan can go right up against the wall without leaving room for the cistern behind it.