Android Q could make the back button obsolete
Android has seldom failed to support a button that allows the user to move backwards or return in the UI - in some versions, it was even a hardware feature on phones. However, according to XDA's YouTube channel, this feature of the OS may be phased out as its newest version hits devices. The outlet has found that the leaked build of this version to which they allegedly have access, replaces the back button with the navigational 'pill'.
This 'pill', which was introduced in Android Pie (or 9.0) and also acts as a kind of home button, is used to navigate a stack of recent apps. This stack is horizontal, rather than vertical as in every Android version previous to it, giving the UI an appearance that may be too similar to that of iOS for some. It works through swiping it to the right, thus acting as a sort of scrolling cursor in some use-cases.
The XDA's 'new' version of Android, known only as Q so far, also uses the pill in this manner, although the animation for switching between apps while this is done has been improved. However, it also allows for the pill to be swiped to the left as well. This switches back to the second most recent app, as a dedicated software, hardware or capacitive button would have done in earlier builds.
Then again, this extremely preliminary build may not necessarily define the finished Android Q ROM. Therefore, we still have something of a wait (possibly until Google I/O 2019) to find out if the back button is really a thing of the past.