I was never that close to the Fuchsia project, but knew quite a few people who worked on it.
My understanding from them was, as much as I can remember it now, something like:
1. That yes, Fuchsia was originally intended, by at least some in senior leadership on the team, to replace both Android and ChromeOS. This is why Fuchsia had a mobile shell (or two?) at one point.
2. The Android team wasn't necessarily on board with this. They took a lot of ideas from Fuchsia and incorporated them into Android instead.
3. When Platforms were consolidated under Hiroshi it brought the Android and Fuchsia teams closer together in a way that didn't look great for Fuchsia. Hiroshi had already been in charge of Android and was presumed to favor it. People were worried that Hiroshi was going to kill Fuchsia.
4. Fuchsia pivoted to Nest devices, and a story of replacing just the kernel of Android, to reduce the conflict with the Android team.
4a. The Android team was correct on point (2) because it's either completely infeasible or completely dumb for Google to launch a separate competitor to Android, with a new ecosystem, starting from scratch.
To work around the ecosystem problem, originally Android apps were going to be run in a Linux VM, but that was bad for battery and performance. Starnix was started to show that Fuchsia could run Linux binaries in a Fuchsia component.
5. Android and ChromeOS are finally merging, and this _might_ mean that Android gets some of the auto-update ability of ChromeOS? Does that make the lower layer more suitable for Nest devices and push Fuchsia out there too?
Again, I was a pretty removed from the project, but it seemed too simplifying to say that Fuchsia either was never intended to replace Android, or always intended to replace Android. It changed over time and management structures.
You got the high drama stories with the timelines re-arranged to fit the narrative :D
Fuchsias underlying goals are to be a great platform for computing. This is distilled in its current incantation into a short tagline on fuchsia.dev: simple, secure, updatable, performant.
The details of how when and where Fuchsia might fit / gets exercised are nuanced and far more often about other factors than those which make great stories. Maybe there will be some of the good stories told one day, but that'll need someone from the team to finish a book and take it through the Google process to publish :D
I worked on Fuchsia engprod for a while. I am still employed at Google and can't talk about anything that isn't publicly available already (which really means anything gleaned from commits to the Git repo).
I think the best way to look at it is like any software: there's Fuchsia The Artifact (thing that is made) and Fuchsia The Product (how thing is used, and how widely). I don't know anything about operating systems, but my understanding is that the engineers are very happy with Fuchsia The Artifact. Fuchsia The Product has had some wandering in the wilderness years.
My understanding from them was, as much as I can remember it now, something like:
1. That yes, Fuchsia was originally intended, by at least some in senior leadership on the team, to replace both Android and ChromeOS. This is why Fuchsia had a mobile shell (or two?) at one point.
2. The Android team wasn't necessarily on board with this. They took a lot of ideas from Fuchsia and incorporated them into Android instead.
3. When Platforms were consolidated under Hiroshi it brought the Android and Fuchsia teams closer together in a way that didn't look great for Fuchsia. Hiroshi had already been in charge of Android and was presumed to favor it. People were worried that Hiroshi was going to kill Fuchsia.
4. Fuchsia pivoted to Nest devices, and a story of replacing just the kernel of Android, to reduce the conflict with the Android team.
4a. The Android team was correct on point (2) because it's either completely infeasible or completely dumb for Google to launch a separate competitor to Android, with a new ecosystem, starting from scratch.
To work around the ecosystem problem, originally Android apps were going to be run in a Linux VM, but that was bad for battery and performance. Starnix was started to show that Fuchsia could run Linux binaries in a Fuchsia component.
5. Android and ChromeOS are finally merging, and this _might_ mean that Android gets some of the auto-update ability of ChromeOS? Does that make the lower layer more suitable for Nest devices and push Fuchsia out there too?
Again, I was a pretty removed from the project, but it seemed too simplifying to say that Fuchsia either was never intended to replace Android, or always intended to replace Android. It changed over time and management structures.