Today 10 years ago I went to Poland to buy a Phone with pre installed #Firefox OS on. The Phone was a Alcatel One, so very shitty. Two years later I installed Firefox OS on my Nexus 5 instead.
It was a very good concept, but sadly rolled out on too shitty hardware so it never caught on.
It would be great, but a big problem that I see with a new, completely different OS is... the apps.
If a new OS not based on Android launches tomorrow, it will have no 3rd party apps, and it will be very hard to catch momentum without WhatsApp, Youtube, Netflix, Spotify, TikTok, Facebook, ~~Twitter~~ X (๐), Uber... all of those apps that most people use their phone for 90% of the time.
It's what killed Windows Phone. There was a period of about 6 seconds to get in on the commercial phone OS game, and it was long gone by the time Windows made a legitimate effort (Windows Mobile phones didn't really count - they were stuck with legacy PDA software).
Honestly, the AT&T exclusivity and the late rollout of the app store (iPhones initially only had the factory apps) were the opening that let Android in.