Along with a new build for the Dev Channel, Microsoft has released a pair of new builds for the Beta Channel; build 22621.730 (new features off by default) and 22623.730 (features on).
For the features enabled build (22623.730), Microsoft is re-introducing a touch-optimized taskbar. The taskbar will be collapsed or expanded based on whether your tablet or 2-n-1 device has a keyboard attached, but can be toggled by swiping up or down on the taskbar.
There's a setting in Settings > Personalization > Taskbar > Taskbar behaviors to enable or disable the feature, if you have the feature enabled the touch-optimized taskbar will be on by default but you can turn it off.
Some more general System Tray improvements are included in the new feature enabled build, but you will still not be able to rearrange taskbar items, although Microsoft has heard the feedback and this behavior is slated to come in a future build.
You can check out all the fixes and changes for both builds in the blog post.