I'm sure there will be problems implementing this.
First they would have to make it so people could not bid unless they actually had what they are bidding.
Second they would have to make it so if you bid, it gives the npc the zeny so that if you actually won you couldn't back out(excessive trolling will take place if this isn't here).
Third they would have to make it so if you didn't win, you get your zeny back(not sure how hard this is to do but, just pointing it out).
Also I'm sure they wouldn't implement this unless there was a token version added also or else it wouldn't see much use since a lot of ingame items are worth more than 1bil and I prefer the auction house they have in Tera. If you've never played Tera you auction off your items with an Asking Price and Buy it Now price. How it works is that people can either offer you an amount, for example 90 tokens for farmor(incase you're offline you will get the offer upon logging in), or buy it right then and there for 95(which was your Buy it Now price). If your item is purchased while offline, the tokens are sent to your storage. And your items stays up there for a week unless it is purchased.
I'm sure the version I explain from Tera would be much harder to implement, but just throwing out ideas.