I still don't see it how they are going to convince the miners to drop the 1MB limit.
Is there even a single mining pool that would not want to see 1MB limit at work, at least for awhile?
When they see it, when they see the size of the incentive the limit gives them, it will make them even more motivated to never unlock it.
Counting on the pool operators that they will just unconsciously start mining version 3 blocks, just because it will be a default setting in bitcoind version 0.8.4 onward...
One would need to think that these people are either stupid or ignorant, which I don't think they are.
But if you're convinced miners would not go above the 1Mb limit, why are you afraid of replacing a hard-coded constant by voluntary/decentralized/p2p/spontaneous-order limits?
When it's time to drop the limit, soft-limits configs should be available on bitcoind. The default first entry could be precisely 1Mb, just to keep as is. Block generators would have to manually change that configuration in order to start easily accepting larger blocks... otherwise they would refuse them until they're deeper.
As you say, they'd likely not change it so easily. They'd only change if they consider the potential extra-revenues from adding more transactions more valuable than the risk of being orphaned - and that's precisely demand pushing for more supply.