Probably not. While some legacy content will be cycled back in, it is highly unlikely that Destiny 1 will be merging with Destiny 2. Bungie took a look at what content was being played and replayed and determined that some content is just not worth maintaining and updating, but the content that does have a high replay value will be cycled back in, over time. Bungie is not looking to simply copy and paste content into the new game; they want to selectively revive older content.