Let me rephrase that. It's not the changing reward that bothers me, it's the huge drop in the curreny's buying power that would come with the application of this system beyond when it's unnecessary, aka the early stages. If 10x reductions in buying power kept happening, people would stop using the coin.
Ah ok I see what you mean.
Those 10x reductions in buying power require at least a exponential increase in computing power. So for a 10 times reduction in value the amount of hashing power must increase to the power of 2. So the network would reach a equilibrium where the coins lose value a rate that is slower by the square of the network hash rate.
So for your coins to be worth less, the currency must as a whole be much more attractive. So you can't just sit on them and get rich but they are holding value relative to network hash rate none the less.
If people decided that the coins were worthless, then the network would not have a increase in power because people wouldn't care as much meaning your coins would gain in value again because more miners have left.
This is the reality for a early adopter: Mine thousands of coins in the first month and expect to get rich. The early adopter does not get rich because now many more people use the currency. However if the adopter kept mining for a few years, those exponential increases in network hash rate have to slow down because its physically impossible to keep increasing exponentially.
(remember a exponential increase in hash power does NOT result in a exponential increase of minting, its far less)
The only time a coin increases exponential hash power is in the first months which is considered a pre-mine by most accounts. This coin would be more equal in that 10% of all coins ever to exist would not be created in the first week.
If you wanna strike rich with this coin you need to mine throughout its first few years until the minting starts to pale in comparison to the overall supply of coins.
Remember the coins cannot constantly keep losing 10% of their value, that would require a exponential increase each time in hash power. Look at Bitcoin, Bitcoins growth in network power is at most barely 30% up each time, most of the time its around 10% increase. If this coin was at the current size of Bitcoin in terms of hash power then your coins would be very very stable. A 30% increase DOES NOT means a 30% increase in coin supply but just 5.4% increase.
And as I would predict, after 10 years the increase in supply would start to slow down in relation to the overall supply. Does this mean early adopters cannot just mine a million coins and sit for 3 years and then just sell them and be a millionaire? Yes, I don't see this as a problem. If you do then your just chasing a get rich quick scheme which is the moto of all the Alternative coins at the moment. Even Bitcoin.