Nova Launcher has been updated to version 5.5 in the stable channel, and this new version brings changes for where users can put search bars, how icons are handled by the launcher, and the ways that popup menus can appear. Specifically, users can now plant a search bar in their dock, which can go above or below their icons. Users can also make Nova Launcher unify and normalize both the sizes and shapes of icons that aren't in an icon pack. Finally, users can now change the style of the per-icon popup menus to the new block style seen in Android 8.1 (Oreo). The newest version of Nova Launcher should be available for all in the Play Store by now, but if you're not seeing it, follow the source link to grab the APK directly or sign up for the beta to see these and other features in beta releases.
The search bar in dock option can be triggered from the Dock section of Nova settings. The search bar won't scroll with your dock, and cannot take any other extra actions at this time. Functionally, it's a normal search bar, and follows whatever style you set forth for the main search bar. Long-pressing on it will allow you to replace it with most any widget you like, as well as edit it or change its height and width. Some widgets won't work in this area, due to their dimensions.
The changes to icon handling allow you to tell Nova to normalize the size and shape of legacy icons, and change the overall shape you want for them. You can choose a square, a circle, a rounded square, a squircle, or a teardrop shape, and all icons will get that shell, so long as they didn't come from an icon pack. The new style for the icon pop-up menu, meanwhile, displays the icon's built-in actions along with Nova's actions for the icons, all in a single Material Design-compliant block, rather than the "pills" for individual options seen in Android 7.0 (Nougat) onward. This visual style apes that seen in the upcoming Android 8.1 (Oreo). Much like the pills, unfortunately, the color scheme for these is determined by your system, and cannot be changed without using a theme engine like Substratum.