It's been a week since Apple released iOS 14.2, so it's time to start testing out a whole new round of updates. Today, the first developer betas were made available for iOS 14.3, iPadOS 14.3, watchOS 7.2, and tvOS 14.3. The only thing missing is a new beta for macOS 11, although to be fair, macOS Big Sur was only released yesterday.
As for what's new, that's anyone's guess. All of the release notes pages in Apple Developer go to a site that says 'Page Not Found'. As 9to5Mac points out, it could include support for the ProRAW feature that was announced at Apple's October iPhone event. In fact, it's not at all uncommon for features not to make it into the initial major release and then show up throughout the year.
If you really want to know what's included, you can either install it and find out, or wait for others to do so. Right now, this is only for developers, but it should show up for those on the Public Beta Program soon enough.