This makes perfect sense really… hot enough hot end glass “filament” once at temp totally acts like FDM printing… (i guess there is a reason why they call it the “glass temp” when talking about filament melting points. 
http://www.dbclunie.com
http://www.3ders.org/articles/20150622-micron-3dp-announces-breakthrough-in-3d-printing-glass-materials.html
if this would work with glass powder that melts and extrudes that would be cool or hot 
Wonder what they made the hot end out of? Titanium just squeaks in on the temp front (melts at 1941 Deg C), is fairly abundant on earth compared to all the other high-temp elements/metals (except carbon), and technically you could 3D print your own nozzle using an SLS machine.
probably some ceramics.
O