Android is very unapologetically Linux and it's unlikely anyone seriously proposed doing anything other than use Linux.
Fuchsia more likely was for all the stuff that Google kept experimenting with using Android just because it was there rather than because it was a good fit - wearables, IoT, AR/VR, Auto, etc...
Other operating systems have emulated Linux so that you can run Linux userland applications on top of a different kernel, WSL1 and FreeBSD are good examples.
Fuchsia more likely was for all the stuff that Google kept experimenting with using Android just because it was there rather than because it was a good fit - wearables, IoT, AR/VR, Auto, etc...