My understanding is that:
- The penalty applies to the block subsidy and not the transaction fees.
- Under constant demand blocks can increase continuously by pushing up the median block size.
- There doesn't seem to be a push back mechanism to confine block size except for reduction of the median by block space exceeding demand.
This means that as long as there are enough transactions waiting, blocks could always get full which would not incur a penalty. However, whenever there are enough transaction fees waiting to add e.g. 0.25% of the block subsidy with 5% additional block space, it would be economically viable to exceed the median block size by 5%.
In a scenario of constant demand excess such as Bitcoin is currently entering, blocks could continuously grow e.g. by the aforementioned 5% per day. Even a consistent growth of 5% per day would amount to 40% per week. As the block space supply could then grow exponentially and essentially unboundedly, all kinds of use cases that require cheap block space would be attracted, in turn creating a practically unbounded demand.
Meanwhile, assuming approximately homogeneous fee levels over the body of waiting transactions, e.g. transactions filling 5% of the block space should not exceed 0.0025 of the block subsidy, otherwise a bigger block would be more profitable to the miner. Hence, short term optimizing miners could have fees trending toward a small fraction of the block subsidy (for the assumed 5% growth it would be 5,25%).
This growth would be further exacerbated by the decreasing block subsidy reducing the cost of block size increases.
With sufficient demand, one would end up with a boundless block size, and a minuscule block reward, a tragedy of the commons. What am I missing?