Edit: Trading Bitcoin for gold is an interesting application but not a "killer app" for Bitcoin. Ever thought of the possibility that Bitcoin could replace gold rather than replace the USD?
I'm not even sure its an interesting application. You have to have Bitcoin or Gold for any interest, for those with Bitcoin its hardly a driver (to get into Bitcoin) and while there's a few goldbugs that like the political aspects of Bitcoin, i reckon they're a very small minority and hardly likely to dump significant gold into Bitcoin.
Which comes to the question just what is the killer app? Well, i'd be rich if i knew, but really the deeper question is what are the applications of Bitcoin, killer or otherwise, and which are even special. Other than the core distributed trust mechanics, i cant think of something that is available elsewhere, or solved by a change to business models or process. So a killer app needs to utilise that which is unique, the distributed trust, the blockchain. That's where the breakthrough will come from imo, an indirect use.
What we do know is there are 700 ounces of gold for every bitcoin.
I know a gold bug who sold his common AU to get into scarce BTC.
Either way the market, if not manipulated or otherwise subjected to fraud, will provide price discovery.
The OP is onto something here. Although coinabul and amagimetals came to my mind as they both buy and sell AU and BTC. Seems to me that they would be in the position to develop the AU/BTC market and give birth to an exchange rate.
Oh and the market will also provide price discovery if governments are eviscerating this innovative market space. coinabul and amagimetals could be stopped dead in their tracks because they are a centralized type of operation.
Any solution would have to be de-centralized?? The thing that springs to mind is localbitcoins.com.
This website combined with that near radio whatever thingy that dating sites are now using.
Bam! anyone anywhere can meet people who are interested in settling a BTC/AU trade. Localbitcoins.com will facilitate meet ups and initializing contact.
my .00000002
BTC I still don't understand how Ripple is anything except "monitor-able gateways". XAU is not physical gold.
Why would i want to use a middle man coin? I don't see the benefit. The whole point of bitcoin is to dis-intermediate.