Why wouldn't miners reject interactions with miners who set the block size too high, for instance?
Yes, I believe they would. So far, most miners and pools are VERY conservative; I think the idea that they will create huge blocks that have a significant risk of being rejected, just so they MIGHT get an advantage over marginal miners that can't process them fast enough, is loony.
Rejections are is
not a significant risk for miners. That's the whole point of my original post on the issue. If your blocks are built upon by the majority of hashing power, you come out ahead in the long run. Your orphan rate does increase proportionally, but if, say, 5% of the hashing power never sees your blocks, the increase in varience is low, yet you get the very real benefit of 5% less competition. In the long run there is no "might" - it's simple statistics, and I haven't seen anyone offer a rebuttal based on analysis rather than hand-waving.
But I might be wrong.
So I'd like to wait a little while, think deeply some more, and see how miners and merchants and users react with the system we've got as transaction volume increases.
I agree with you there. But if large blocks turn out to not be an option, for whatever reason, we need alternatives, and creating those alternatives take time. We've probably got two or three years before the limit becomes a big issue, maybe less, and as you know raising the limit will take at least a few months for the consensus to be achieved among all users. Right now what I'm hearing from you and Mike Hearn is a defacto "yeah, we'll just keep upping the blocks size, I just don't know yet by how much or if it'll be one-time thing or a floating limit". This attitude leads to people not working on alternatives and if alternatives don't exist by the time the limits are reached, like it or not, raising the limit will be the only option regardless of the downsides.
You already know about the fidelity-bonded banking stuff I'm working on, but it really bothers me that I don't seem to have much competition. Frankly I'd be happy to see someone else come up with an even better idea that I haven't thought of, or just come up with a better implementation of bonded banks than me. That outcome is much more likely to happen if you make it clear that if off-chain value transfer systems are developed not raising the limit
is an option.