Reading tea leaves
I expect that google wouldn't undertake another platform this late in the game if it thought that it's existing ones filled, or could easily be made to fill, the hole.
Android has been hugely successful and Google is in may ways a victim of it's own success. It doesn't control it's own platform as a result of forks, platform fragmentation, and major stakeholders that drag their heels at every turn. It has also been the victim of it's cavalier tendencies toward others IP, especially in it's earlier days. It's having to pay lawyers to deal with the hole they dug for themselves in gluing Franken Java on top of Linux during the glory days of YouTube piracy.
Chrome OS was a transparent ploy to push the market into an all browser, all of the time world. While the Chromebook hardware is pretty good, the fundamental limitations have limited it to the niche it currently fills, mainly running Google apps and web surfing. Despite the Chrome OS teams aggressive cheerleading both inside and outside Google it hasn't been able to push far into the desktop space. If management wants an escape hatch from the hugely popular Android, the door doesn't look like Chrome OS. The Android Java application layer was their last, best attempt to salvage ChromeOS market share, and that's running INTO the fire.
Fuchsia lets Google reboot Android with a modern kernel and application layer. They can create a playing field without carriers and OEMs dragging their heels on OS patches and upgrades, and without Oracle IP and licensing hassles. They have a good team, and if they can execute they will be in a good position, as they were in with Android, catch market share as people move from Desktops and Laptops to tablets and phones. VR may or may not be the next big thing in general computing, but people aren't going to be lugging laptops around much longer. I just hope they fix the play store this time around, or their going to give the game up to Tim Cook.