Really interesting quick talk on PayPal's migration from Java/C++ to Java/C++/NodeJS by Cristiano Betta.
Lots of organisational context to the change and a honest statement that performance improvements and reduced developer overhead is probably the result of addressing historical tech debt rather than purely a single tech change.
Using open source is important to attract and retain developers.
Server-side Javascript is more about encouraging developer to move around the stack rather than siloing developers. It also removes the disconnect between the prototyping teams and the production environment.