`+` is checked for overflow by default (can be overridden with compiler flags), and `&+` is overflowing addition and does auto-vectorize equivalently to C++.
I'd be quite interested in seeing a benchmark comparing checked and unchecked addition that doesn't get auto-vectorized to understand the performance in practice for non-numerical computing.
When I first approached writing this article, I had a hard time. We have learned a lot from other companies sharing their experiences and we wanted to give back. We are doing this now because we think we have enough content to regularly write posts that will be interesting to other developers. Although we are very interested in open source projects and giving back, open source projects require significant amounts of time and energy (something at a huge premium). Because of this, we have instead adopted a policy of open source snapshots (see the README at: https://github.com/coursera/js-libraries-snapshot) for code contributions, as well as sharing what other lessons we have learned through other channels. I have spoken at AWS re:Invent, as well as written about other successes at betacs.pro, my personal blog.
As for your warfare speculation, I am happy to say it is just that. We have not had any warfare whatsoever here at Coursera. That simply is not our style. Instead, we tried out a variety of different programming languages. Through organic internal growth, we have come to adopt Scala and Play! not because of a decree but because we have found it helps us get the most done quickly, and reliably.