What exactly is the driving force behind the desire to do everything in Javascript? Is it just because we have a surplus of Javascript programmers? It doesn't seem to me that this task is particularly well suited to Javascript. (I think) Something like Erlang would be more applicable.
And to me it seems that learning a new programming language (even one using a relatively obscure syntax), is a much simpler task than designing an entire project (or piece of a project), around a language that doesn’t really fit the needs of a project.
To that extent, I think that the idea of a ‘lingua franca’ language is an inherently broken metaphor. Programming languages are closer to human-computer interaction tools than they are natural languages. ‘Lingua franca’ implies that every language can communicate approximately the same thing (it is just a matter of who has influence). I think this is a mistake, as different languages allow you to think in hugely different ways about programming. Different languages have different intrinsic concepts.
It may be that this argument boils down to ‘if all you have is a hammer, everything looks like a nail,’ but even that is an oversimplification, as I don’t even use the same hammer for all types of nails (tack hammer, framing hammer, etc).
I am not saying that node.js is necessarily a bad thing to have. It may turn out that Javascript is indeed particularly well suited to this type of application. Superficially, however, nothing convinces me that this is some sort of exciting home-run-win situation (or that it is any better than any other functional-style programming language).
Could you explain the excitement and appeal to me?