Unless the new Wordpress is written in node, comparing the new “JavaScript” stack with the old “LAMP” stack makes no sense to me. Those technologies do not serve the same purpose.
It's written in JavaScript; it runs on node.js - at least the front-end part of it (https://github.com/Automattic/wp-calypso). I don't know what is running on the backend but I don't think it's LAMP?
The point I was making though is that "WordPress" can mean two different things - wordpress.org (the self-hosted LAMP version) or wordpress.com, which is a SaaS offering (so the language is more or less irrelevant unless you're really interested in running your own admin frontend, I guess).
Calypso is our JS dashboard that lets you manage all your sites in one place, plus get cool WP.com features like stats and notifications. It's just a REST API client, just like the iOS and Android apps.