Despite what was said on stage, Google confirmed to
AndroidAuthority that they won’t explicitly disallow third-party gestures. Instead, Google sees third-party gestures “as a power user option.” Thus, while OEMs
will be forced to offer the traditional 3 button navigation
and Google’s new gestures, they
won’t be restricted from offering additional navigation gestures options. Users will choose between the 3 button navigation mode and Android Q gestures during setup, but it’s unclear whether OEMs are allowed to show their own gestures during setup.