Here's apartial lost of new features coming to preview program (stolen from
http://majornelson.com/2016/03/01/coming-to-preview-buy-xbox-360-games-on-xbox-one-16-person-party-chat-and-more/):
Here’s what’s coming to Xbox One Preview:
– Purchase Xbox 360 Backward Compatible games on Xbox One: Fans have spent more than 30 million hours playing Xbox 360 games on Xbox One and so it’s natural that being able to purchase Xbox 360 Backward Compatible games on Xbox One ranks as one of your top requests. With this update, you’ll be able to do so! Find and purchase Xbox 360 Backward Compatible games the same way you would Xbox One titles and, once purchased, Xbox 360 Backward Compatible content will automatically download to your Xbox One and be ready to play!
– Include Party Chat in Twitch broadcasts: A top voted-for feature on Xbox Feedback, Xbox One Preview members will be able to broadcast Party Chat when using the Twitch app. If you are broadcasting from your console and in a party, you can invite other people to include their chat audio in your broadcast. If a member of your party declines, they’ll still be able to chat in the party; they just won’t be heard in the broadcast. Additionally, as the party leader, you have the option to mute a party member’s chat audio, even if they opted-in. You can also include party members on Windows 10 PCs in your Twitch broadcast.
– Output your Party Chat to headset and speakers simultaneously: Xbox One Preview members will be able to select their preference for where Party Chat audio is heard: their headset, speakers, or both. To do this, go to Settings – Display & Sounds – Volume.
– Customizable Game DVR recording length: Based on Xbox Feedback, it’s clear that fans want to be able to configure the length of their Game DVR recordings. Currently, Game DVR recording is fixed to a 30 second duration. With this update, Xbox One Preview members can adjust the recording length to 15 seconds, 30 seconds, 45 seconds, 1 minute, 3 minutes or 5 minutes. To change the preferences, visit Settings – Preferences – Game DVR & streaming.
– Track Achievement progress in the Xbox One guide: We’re making it easier to access your Achievements by including them in the Xbox One guide. In the new Achievements area you’ll find a quick link to see all of your Achievements and you’ll be able to track your Achievement progress in real time directly in the guide, without having to snap a separate Achievements app.
– Video playback directly in the Xbox One Activity Feed: We’ve made improvements to video playback in the Xbox One Activity Feed. Xbox One Preview members will be able to play an entire video inline rather than having to leave their feed to launch it. You can even ‘like’ the video while previewing it by pressing X. Preview members will also enjoy new pause, restart, and full-screen playback options, when they do choose to launch a video from their Activity Feed.