We might have a takeoff that does not involve a transition to what we'd call general intelligence. All the AI needs is an ability to optimize very well in one area that is critical to human civilization -- warfare, financial trading, etc -- and the ability to outwit humans who try to stop it.

There are ways that the AI could prevent humans from stopping it without the full smartness/ trickiness/ cleverness that we imagine when we talk about general intelligence.

Although I want to avoid arguing about stories here, I should give an example, so imagine a stock-trading AI that has set up its investments in a way that ensures that stopping it would bring financial disaster to a wide variety of powerful financial entities, while letting it continue would produce financial benefit for them, at least to a certain point; and that this effect is designed to grow larger as the AI takes over the world economy. Or more simply, a military AI that sets up a super-bomb on a tripwire to protect itself: Nothing that needs 1000x-human-intelligence, just a variation of the tripwire-like systems and nuclear bombs that exist today. Both these could be part of the system's predefined goals, not necessarily a convergent goal which the system discovers as described by Omohundro. Again, these are just meant to trigger the imagination about a super-powerful AI without general intelligence.