New Google Sites has been released for everyone. This release is intended to allow people to try out the features and see how they work. The most used features from classic Sites will be incorporated gradually, while not ALL the features will be re-introduced Google is constantly monitoring the feedback and prioritizing heavily used and top requested features. Please make sure you send feedback to Google to make your feature requests and bug reports.
Sites Help now has sections for classic sites and new sites. Select the correct area as shown in this image: