Well other chains might have other methods to deal with this problem.
But in BTS, specifically, what if witnesses detected the spamming and simply didn't include those transactions on the blocks? I mean, this would be a very serious action, they would need to be sure but... Or why not make fees escalate if they're done within X blocks? That makes sense? If number of tx > X and the transaction IDs are all within [w, z] blocks, they scale up.
If it passes that defined threshold then fees go up OR transactions get delayed and spread throughout the next X number of blocks as a mean to distribute it evenly