I don't think it is. I seem to recall Isaac saying that he considers require.extensions to be a mistake, though I don't know if he meant the concept (extensibility) or implementation (register hooks under filename extensions). Either way, I think it's recognized that a lot of people enjoy and use the functionality so it's unlikely to go away.

As an aside, here's the relevant bit of code that loads the (already compiled) source as a module: https://github.com/joyent/node/blob/master/lib/module.js#L40...