@raucao article explains "Google promised to share this [system to install Web Apps that integrate well with the system] with third-party browser vendors" but hasn't followed through.
In a healthy and robust mobile ecosystem where a Mozilla-like org (read: multi-vendor coalition) is a major force providing a viable de-Googled Android and can be relied on to do the fair, reasonable thing contra Google's self-serving/unpopular decisions re Android, no one would need to rely on such promises.