I don't follow JavascriptMVC, so I couldn't give you an answer there, but as far as canjs goes, mustache is receiving a LOT of love in comparison to EJS. There is just a lot of functionality in EJS that makes it ill-suited for templating, and I wouldn't place any bets on it's future capabilities. There is a lot of work going into making mustache obscenely powerful in canjs, and they're actually in the process of developing some pretty exciting new mustache capabilities that could significantly increase the performance.
Personally, I'd like to see CanJS go in the direction of dropping support for EJS altogether, or at the very least announcing a clear roadmap for EJS. Right now I suspect that can.Component won't ever be supported by EJS, however that hasn't been made clear.