Am I missing something?
1) You are missing that miners are interested in fees. They have a right to include/exclude any transaction.
2) You are missing that it is almost impossible to upgrade relay policy on thousands of nodes.
BTW. This is funny test.
Miners just raised the minimum fee, leaving a lot of unconfirmed transactions and screaming users.
Blocks are not filled.
Right now mempool on
https://tradeblock.com/bitcoin/ is 12mb (note: transactions with a fee less than 5 satoshi per byte are ignored)
https://en.wikipedia.org/wiki/Tragedy_of_the_commons Edit:
3) Since the start of this stress test the price on exchanges rized up. Everybody likes it

Are you sure that you really want to fix this issue? A lot of people would vote against

I've been just speaking about the default policy in the "Core" client.
In this sense, fixing the issue is trivial.
After such an update miners/ relay nodes are of course still free to run any code they like -
nobody forces them to update their policy
Edit: All I'm saying is that it is easy to make this kind of attack as expensive as the "traditional" block-size-filling spam attack. I'm surprised this is not done yet.