Red/green zones or just about any partial/segregated lockdown seems likely to not work. Being in a red zone is worse than being in a green zone so people are incentivised to move from red zones to green zones (if they can). This is not what you want. It seems hard to restrict movement or enforce a strict quarantine in countries that are generally not planned to support restricting movement across internal boundaries.

I doubt this. It was spreading the Bay Area in late December. The first reported case with local transmission was in late February. That said, we weren't really looking for it, but without incredibly widespread testing, they best we can do is keep it lurking in the background.

The longer it's allowed to persist the more social and economic damage.