And what about having nodes build in some sorts of max block size relay delay, so they can punish miners that in their eyes produce too large blocks?
there are things that can be done to disincentive miners from attempting to break that limit when it suits them. Did you not understand what I was trying to communicate concerning adding a 'soft limit' propagation rule to the clients? Truly harmless to the network and the client, and only somewhat damaging to the miner, unless a significant enough of a minority of clients participate in this rule, and the miner with an overlarge block ends up with an orphaned block as a direct result. It doesn't have to work every time, just enough for the miners to notice.
It is also truly harmless, that is, utterly uneffective in influencing them in any way, to the big miners.
Sure it might impact miners who are too small to have direct dedicated high bandwidth pipes to the top 51% miners, but the top 51% miners will not even notice if every one of you irrelevant non-mining nodes all stick your heads in the sand at every block on the chain. You just don't matter to the big boys, the most you could do would be help the big boys to shake the small players out of the game faster.
-MarkM-