I tend to agree that the payback probably wouldn’t be worth it, but it would be cool 
I used to love cloud9 because it meant I could play with Meteor even inside my corporate firewall when I had a spare 5 mins…
Cloud9 and cloudpebble are both on github, so might be a good starting point if it ever was attempted.
Deploying from github and a free-tier on Galaxy would get you almost as far with much less effort.
Trying to integrate with JSFiddle/Codepen/CodeSandbox would be an interesting challenge though. CodeSandbox has a node template, so that is prbably the best starting point. Looks like someone has already succeeded… Maybe continue that conversation is this thread…