The OS Fuchsia, including the kernel Magenta, appears to be open source, mostly under BSD 3-clause, with parts of the kernel under MIT and similar licenses.
Open sourcing the product will help the competition to catch up quickly, all they have to do is take googles product and change its look. The next half is infrastructure, which companies like Microsoft, facebook, amazon, alibaba all have. Plus services like AWS will help future version of dropbox & netflix.
A good example of that is Visual code. I am sure some at github (atom's paprent) is pissed.
https://fuchsia.googlesource.com/fuchsia/+/master/LICENSE
https://fuchsia.googlesource.com/magenta/+/master/LICENSE
https://fuchsia.googlesource.com/