As a long time writer of JavaScript I say bring it on. If you want JavaScript to succeed outside client browsers in a big way you must to consider performance. If it wasn't for incredible perf gains in the past couple of years you would not see JavaScript pushing into the server side.

However JavaScript performance still leaves much to be desired - http://stackoverflow.com/questions/6216888/is-nodejs-faster-....

I want JavaScript to close the gap without sacrificing dynamism. And it won't - these feature are entirely optional and they free the implementors to make assumptions which allow further optimization.

"Pay for what you use"

To be totally honest I don't see myself writing plain JavaScript much longer, I'm closing in on 7 years now. At work I use quite a bit of CoffeeScript and very likely in the near future I'll leverage ClojureScript.