Thanks for your comments. There's a certain level of "know your audience" I'm trying to leverage here, and I think you might have picked up on it. I suspect certain developers already heavily use some kind of docker strategy to speed up iterative development. But those developers also rarely use iterative cycles for most of their daily work. In other words, they know exactly what they want and fast-turn-around-per-line-of-code isn't important.
But when it is important, getting that code to execute when there's nothing in the blockchain is a huge (or just expensive) roadblock. I happen to know that one of the design goals of tinman was to allow deploying a testnet with a sample account list. But that requires a good amount of time to prepare. Thus, the only real bottleneck in this strategy is how long it takes to compile because the 2,000 sample accounts are delivered as part of the tintoy docker image.