I guess it depends on the situation of the company. But I guess that before doing such movement, company should do a pilot to verify if introducing Go can solve currently existing issues (with development velocity, bugs, performance etc.). After that answer should be simpler :)
> Two key aspects to that question: whether/when/how to re-write existing systems in Go and how re-written or new implementations integrate with the existing ones. It also really depends, but from my experience companies that were switching to Go were keeping legacy part and people who were able to maintain it. In the meantime they re-written what was worth to be re-written. Without touching old part too much.
In that case yo can stay with a situation where you have some developers of old technology and some of the new one. But AFAIK it was not a major issue.