They have been talking about trying to add multicore support for years now, I highly doubt anything will come about it. If anything someone will find a way to use a plugin to "hack" a half way fix for core support. Java just isn't made to support it.
Java IS supportive of Multithreads. There are plugins already using this. Like dynmap, and many others. A hack wont work. The multithread support needs to be coded in on the botom level of the java application.
I had conversations for hours and hours with java devellopers about this and there is NO way you can add multicore support without rewriting minecraft.
And before anyone is gone rage in here with " i run on multiple core's" That are sertain mods and plugins than can shift there load to a different core. But the main minecraft core with all the rendering will stay on one thread.