It's my understanding that the Plan 9 compilers were ported to linux and used to compile early versions of Go. Past that, the only connection is that one of the Go project leads used to work for Bell Labs.
Fuchsia doesn't share as much of the story but does pick up where in Dante's Inferno the original Unix people tried to abandon the root user to redeem themselves almost 30 years ago. Combined with capability based model last seen deployed in the wild with OS/400 and Burroughs machines before that, it would be the first truly new OS in decades.
Although it would be wrong to consider Go as a derived product of Plan 9, I think it is right to call it its intellectual successor (although not the only one).