These are fairly obscure pieces of kit, which suggests that while Google has no beef with external developers getting inside Fuchsia and having a look around, it's not going to be easy for them. It'll run on open source emulator QEMU as well, but the graphics stack needs Vulcan support, which QEMU doesn't offer, so you don't get the OS interface, just a command line.
Getting it going on the Pixelbook isn't any easier. The installation guidelines recommend installing it with a USB drive, but warns that the process is "destructive" to the USB device. Allegedly this just means you'll need to reformat it, but again, the wording, and the choice of supported devices so far, means Google isn't actively encouraging people to have a go at this stage.