I just don't see it being logical to have it going anywhere near 500k/block.
I like our current method.
Once all the blocks are mined, the pools can force a minimum transaction fee to be allowed by them.
I do think that 21million coins is a LOW amount, but that's why there a numbers bellow 0 (to the 8th).
500k/block would be necessary if 300,000,000 people used it. That would keep the currency at roughly parity with the dollar (which makes sense, in order to avoid the psychological "less is not more" barrier).
It is also necessary to continue with block rewards, so that the currency doesn't go into a deflationary spiral (which WOULD happen - see "The Great Depression").
I also believe that, with the current Bitcoin client, transaction fees will not be high enough to maintain a sufficient number of miners to keep the network secure. Once we hit 25 BTC rewards, the number of miners will drop in half. Same thing when we reach 12.5 BTC rewards, etc. The end result is that we wouldn't have enough money being spent on mining to keep the network secure, which I'll explain in further detail.
If we assume there is no growth in bitcoins from now until the reward is effectively gone (and thus no value increase), then miners will see a reward of 0.05 BTC/block or so. Which means that the network would be secured, theoretically, by 1/1,000 of the number of miners that currently secure it. We'd have 20-50 GPU's securing the entire network worth $210M. In order to maintain the same level of network security that we have today, on a "hash-per-market-cap" basis, we'd have to have 1000 times the number of transactions in each block that are currently had. That's just not going to happen unless worldwide adoption becomes a reality, so we will always have a discrepancy between the hashing power securing the network and the total value of the network. Sure, if prices reach $1,000, then we might have 2,000 to 5,000 GPU's securing the network, but that network would be worth $21B. So 2,000 to 5,000 GPU's probably isn't going to be enough at that point either.
At the current transaction rate, the network will not be sustainable in the future.See the problem?
It's been suggested a number of times before under Inflatacoin, Keynescoin, etc. Nobody has cared enough about the idea to actually spend the time creating the new chain. People wouldn't buy or mine it because with inflationary currencies you either use it right now or you lose your purchasing power, and since there would be nothing to buy with it then the only option is to lose.
It's not inflationary - it's stable. Well, eventually anyway.
Once the number of coins generated equals, roughly, the number of coins accidentally lost, then the currency is stable. It shouldn't increase or decrease in value. Up to that point, it would be inflationary, but the hope would be that the adoption rate of the currency would keep up.