Microsoft might have "embraced" open-source, but we'll see in a few years time if this was truly to help open-source or if Microsoft was merely a wolf in sheep's clothing attempting to infiltrate and conquer - my gut-feel says this was Steve Balmer's agenda and that they are trying to change, but I'm still hesitant to just accept that they completely changed over night.
Personally I'm not sure about ChakraCore, it feels like they're trying to chip away at V8's market share and if ChakraCore is not maintained properly, you'll get the same problems that IE caused on the client side, but on the server side.