Without generics, GUI toolkits, good quality SQL drivers from the vendors themselves, enterprise frameworks and the IDE quality of Java and C#, Go will never be an actual threat to them.
Go 2.0 might be, if it ever happens.
According to Wikipedia [2] same period for JDK 7 to JDK 8 was 1 year. Also on the same Wikipedia page, you can see how many bugfixes JDK 8 received in that 1 year.
So JDK8 to JDK 11 release is also going to be a little bit risky as people will need to depend only on 3-4 months stability reports to upgrade their production deployments to JDK 11.
The bi-annual releases aren't for companies to upgrade to every 6 months but for power users who like to experiment and try out new bleeding edge features. Same as with Ubuntu releases for example.
Both the languages and platforms are very good. But right now there is more influential OSS (HBase, Cassandra, Kafka and many others) stuff in Java. However, I wonder with Oracle's new stance, if C# will become the preferred language for Open Source. Or Maybe Go will leave both Java and C# behind.