This is a hardware thing so it will not be coming to previous Pixel devices or any other Android smartphone. But two things which you can get right now from Pixel 4 on your Android smartphone are the Pixel exclusive Launcher and live wallpapers. A lot has been leaked about Pixel 4 lately including the launcher and the official Live wallpapers so you can grab them now and install them on your phone.
Pixel 4 launcher
The Pixel 4 Launcher is obviously based on Android 10 and you can only install it on your smartphone running Android 10. The new launcher from Google Pixel 4 is similar to the previous one Only for one feature. You will get the swipe down to pull notification drawer feature which was not available before. Download here
Pixel 4 Live Wallpaper
The live wallpapers on every new Pixel smartphone are new and fresh and this time is no exception. There are a bunch of new live wallpapers which has been leaked and some of them are interactive. The default wallpaper is Compass which has a little needle in the middle which acts as a compass. Another one is a Doodle where you can create your own wallpaper and set it as Live wallpaper. More wallpapers are just an ariel view with some small live elements like birds and clouds. Download here
Pixel 4 Recorder
Google Pixel 4’s Live caption feature has been leaked recently and Google isn’t leaving it there only. The recorder app in Google Pixel 4 is going to transcribe your voice recordings and save it on your phone. You can search for a particular word or sentence which you have said in the recording. You cannot use the transcribed text for now but it might be possible when Pixel 4 will come out. Download here
Wrapping up
These were the leaked apps from Google Pixel 4 which you can install on your phone and try right now. All you have to do is download the apk file provided and install it on your phone just like any other apk file.