Couldn't this argument be applied to any living thing, not just the ones that humans have engineered? As soon as anything can mutate to enter a new niche, it will work the same way as this would.
Also mutations, often have to overcome obsticles to conquer a new niche. They have to reach a specific habitat or deploy seeds at a distribution system (cars driving dirt roads e.g.).
Lets take a nice little SciFi Example- NASA breeds in its lab a terraformer for venus, a sort of airborn spirondella. This could potentially wipeout all live below, by covering a planet with green "living" clouds.
Now this organism could escape the lab, bot as long as it does not reach a warm, wet climate it is dormant. So even if this dangerous organism was out there- it could potentially deteriorate before it reaches the equatorial belt and starts to bloom.
Nothing is certain in nature, but one thing- if its a success - it trys to be a exponential success.