Node tends to do a better job over Ruby in terms of throughput on the server in addition to the lower disconnect. If you're going to use separate tooling for the supporting services, I'd probably lean to Go over Ruby/Rails simply for the better scaling than either Ruby or Node, but creating a disconnect for a less-performing server stack, I don't get.
Personally, I prefer node coupled with the front end, even if services farther back are using other technologies, being able to tweak your app's api surface to suit your needs in the same language is a much lower disconnect. Just my opinion, ymmv, but if you're already using a JS heavy front end, then a more tightly coupled backend makes more sense imho.
