D&T even when I'm arguing with you I can't help but admire the usually informative technical specifics you include in your posts which I appreciate. However, for the points I award you there I must dock you some for imagination.
Yeah that isn't a solution. So the attacker simply DDOS the centralized point (or few points) of failure.
DDoS isn't a 100% effective or sustainable attack even with a motivated attacker and profitable target. While a target like MtGox might be profitable a site/node simply relaying mining data wouldn't seem so. But even if DDoS was employed it would be much easier to defeat than a traditional target, because you can know
exactly which IPs are friendly and which to block. Remember honest miners wanting honest data have incentive to get it quickest. Problem solved.
For example time zero your node is notified (either directly or through so easy to take down centralized MBR what has to happen before you validate the block and begin work on a new one. ...
Today with relatively low tx volume the time to validate a block is sub 1 second but as block sizes grow (think hundreds of MB and hundreds of thousands or millions of transactions) that time will rise.
Here we see things differently. I've participated (with some stress) in many block size debate threads. I really have trouble seeing block sizes at hundreds of MB being actually implemented in the near future. I endorsed Gavin's proposed course of a simple infinite raise allowing the market to sort out the rest, but I'm less than confident we'll see that adopted soon. His recent public comments on the issue seem to reflect my thoughts.
I think we're more likely to see either no change and more reliance on off-chain txs and alt-coins to relieve scalability pressures and/or a modest increase (say to 5/10 MB once) or modest increases at future points.