A brand new Pixel Launcher UI has been spotted at Google I/O during a sandbox session on Instant Apps. We've not seen anything official about it yet, so it's either going to be debuted soon, or somebody messed up and it's not even a fully tested product. It seems the unreleased launcher was being used to demo new functionality relating to the now more widely available Instant Apps, which it can show in search results alongside those on the Play Store. Previously, the launcher could only display apps already installed on your device.
Thanks to 9to5Google, we have two videos showcasing the new Pixel Launcher that you can view below. As you can see, perhaps the biggest change is that the 'G' search pill is no longer present. Search has been moved entirely and now appears as a translucent gray search box situated at the bottom of the screen, below the row of icons in the dock. It has also returned to its former, full-width glory, but maintains the rounded edges introduced with the pill.
This makes absolute sense to me. Search is such an oft-used feature on any launcher, and with phones getting ever taller it's logical to have it as easily accessible as possible. The pill's location in the top left hand corner of the screen was literally the worst place it could be for a right-handed user, and that decision seemed to be based purely on signifying Google Now was still present one screen to the left.
The very top row of the launcher is now reserved just for the date, although I would hope that weather will also be incorporated into this space at some point. The current version of the Pixel Launcher started to also display the weather in the top right corner after a short period only showing the date. It would even make sense to present other contextual information in that top row, like upcoming events or reservations - basically anything useful from Google Now. If that's not already in the pipeline, let's hope someone at Mountain View reads this.