This would be a very useful feature, and not hard to implement. In fact, it was already implemented and perfectly functional, it is just a matter to activate it.
Someone may argue that this could make us overlap too much with PPCG. I disagree:
- If someone post a PPCG question here, it is off-topic. Adding this feature would not change this fact.
- The presence or absence of this feature do not makes a PPCG question on-topic.
Someone may also argue that this feature invites some sort of abuse. Again, I disagree:
- If someone post a question that abuses the code-snippet feature, it would probably already be a bad question regardless the presence or absence of this feature.
Further, if someone really needs code for a puzzle question or for an answer, he/she can already just go to jsfiddle or ideone and post a link without this feature, or simply copy-and-paste it in the question/answer and ask for people to run it. So, the absence of this feature is not stopping anyone, but the presence would only makes things easier.
I really see no real reason against it.