this assumes that steemit.com would not be DDOS. Since this is the main entry point on the Steem blockchain, this would be an issue.

You also assume that the block producer won't be ddosed and can reliable tell an order, which I doubt.

I think your example is taking too many shortcut to work. In real life I assume it would take more than one block to settle down.

But overall, I think we wouldn't be bloated more than, worst case IMHO, 30 minutes. It is interesting to see the different proposal for ICO(eos, new smart contract standard,...)