sound like the topic of the threat of 51% attack! It is resolved by the big miners's self adjust. when their hash power exceeds a certain level, they will voluntarily shift some hash power to other small pool!
As seignorage declines it will become cost-uncompetitive for transactions.
I don't think the transaction fee will be increased to become cost-uncompetitive when seignorage declines!
In case you don't know what seignorage is (like I didn't), I Googled it and it appears to be the "cost of making money" something like that.
I don't think it's fair to assume that the transaction fees won't be increased. I assume the bitcoin community will always do what is good for bitcoin.
If that includes fee increases or decreases, we'll see, but I do agree that the fees would only increase if that was a good thing for the miners. So if they were to do anything to harm the community (and thus price), it would ultimately hurt the miners. So we'll see how much blood is squeezed from the onion.
For now, the fees remain a very small fraction of the mining revenues, so I suspect we're debating about 10-20 years from now at least... what a problem to have if we make it that far!
