For me, too much trust required. Need to trust the physical gold depository. Need to trust that 'digital gold' will not be issued in excess of physical gold. These are big enough barriers for a new entity. But even if all that is on the up&up, need to trust that some government won't come in, guns blazing, and confiscate the gold.
See e.g. Liberty Dollars for precedent.
yep. dont trust some people that promise to hold YOUR money/gold/
BTCby the way: search for "e-gold"