Sometime down the line, a NAN-spidermonkey or NAN-chakra project might become feasible.
On paper. In reality, HELL NO. I maintain node native addons, and the thing is, NAN is great, but they simply cannot foresee what will break next in v8.
Once something breaks, they provide a node-version-independent feature-shim, but every time there's a new version of Node, I DREAD the work I'm going to have to do to maintain my add ons.
It's simply less work to cross compile C++ to JS w/ Emscripten or write it in JS (or higher level language and compile to JS) in the first place.
Is your lost.
They hope to merge it back into upstream, that seems possible given the recent history of the Node.js project.
Of course, it is very very unlikely that npm modules with native code work in Node.js/Chakra just yet.
I would hope they follow the same path as the jxcore+SpiderMonkey team so I don't have to worry about which engine my npm modules support.