Transaction fees for smaller transactions Thinking about the potential problems with Bitcoin, I am doing a thought experiment.  Suppose that Bitcoin is successful in replacing gold.  The market cap of gold is $9.6 trillion (10^12).  At that level, each bitcoin would be worth $400,000.  In such a world, let's suppose that people were making $40 transactions to buy things.  Then the average transaction would be  0.0001 bitcoins.  Assuming a reasonable transaction fee of 1%, this would imply that transaction fees should be 1 micro bit-coin in such a world.

Bitcoin-qt would clearly need to adapt to this.   Some miners (payment processors) could offer different terms,  and users could choose these payment processors with the addnode option in bitcoind. 

I just wanted to get some feedback on how transaction fees are going to adapt to a higher marketcap.

Kind Regards,
  Harold Naparst
The default fee is in place to decrease the chance the creation of dust outputs (miniscule amounts of bitcoin). Dust outputs cost more to spend than they are worth themselves and they still need to be stored in the disk space of anyone that stores the complete blockchain - thus are frowned upon.

To read a discussion on that matter with some of the Core Developers you might want to review The minimum transfer fee is not trivial anymore.

Currently, there are some mining pools that accept transactions even without transaction fees. The default transaction fee in bitcoin-qt has been lowered before when the value of bitcoin increased sufficiently to make the recommended transaction fee too high. This happened for example in May 2013, when the default fee was reduced to 0.0001 BTC from 0.0005 BTC.

It is therefore expected that the default transaction fee will be kept at a respectively low level should the value of bitcoin increase dramatically. In any case, anyone can choose to ignore it by changing the settings of their bitcoin-qt.