Settings in the Android 8.1 Developer Preview has added a top search bar, which not only displays as a more visible search bar but it stays persistently at the top of the settings page as you're scrolling through it. Google's decision to change the look for the search visually is not just about aesthetics, but with the new look it does seem to stand out a bit more than before and this could very well help more people make use of it. The fact that it stays on top even when you scroll down from the top of the page is certainly a convenience factor as you won't have to scroll back up, but this could also be viewed as a way to keep the flow of things smooth, which sort of makes using the settings search bar in Android 8.1 more efficient and it can help you save time, and that's never a bad thing.
The search bar for those that can't really tell the difference now sort of appears like a long narrow card like you would see inside of the Google app, or like the search bar widget you could place on the home screen. It has a clear defined shadow effect that's been applied around the entirety of the bar to help it look elevated and layered as well as completely separated from the status bar, whereas in Android 8.0 there was a search button, but it was more or less attached to the header and was less defined.
Google's change/addition of the search bar in settings is one that feels like it's about simplicity and convenience, as Google often tries to make using its products, software, and services as easy as possible for the user. Depending on how much time you personally spend in the settings menu, you may or may not find this change a worthwhile one, or one that is too exciting. If you're constantly digging around in settings, or if you're still getting used to the differences in the settings from Nougat to Oreo, then you may find the search bar to be a really nice change, as it can certainly help you find everything in the menu much more easily.