Twitter users are reporting that the company began emailing people who haven't yet signed up for a Vine account—and the emails started coming just hours after Instagram's release of their new video feature. The emails promoting Vine haven't been sent to all users, but many of them who received the emails took to Twitter (of course) to announce what was sent to them; and the timing of those emails could only mean that Twitter feels threatened. As they should be.
Instagram's new features more than double the recording time that Vine allowed, coming with 13 filters and image stabilization. Most importantly, and intelligently, the feature didn't come as a separate app, but simply as an update. That was Twitter's first mistake by creating Vine—they had to get millions of Twitter users to sign up for Vine instead of just giving them the feature in Twitter straight up. Hence, the emails being sent out now.
But, Twitter says that Vine will be getting some "exciting new parts" soon, so we'll see. But it seems to be a little too late for this experiment.