For example, in a movie with a busy action scene involving gunfire/helicopters/storms the production audio is usually useless because there were fans and other loud machinery on the film set to create visual illusions of powerful winds and so on. In this situation the audio is either not recorded or used only as a guide track to match timing on a high-quality track recorded later in the studio. Actors hate re-recording dialog by lip-syncing in front of a screen and producers hate paying for it. This solution is already good enough to use for incidental characters in scenes that are going to be noisy anyway. I give it about 5 years before it's good enough to use in ordinary dialog scenes - not for the intimate conversation between the two Famous Actors flirting over a romantic dinner, but fine for replacing the waiter or other background characters.