First off I think it is awesome the changes that have been happening at c9 for both previews and multiple ports. Moving from c9.io to c9users.io and allowing the multi port binding is just fantabulous. (Yeah that’s my favorite made up word).
However I think there is something that can take this a step further. I work behind a corporate firewall and proxies. Thus I can only access the base preview url like (workspace-name-username.c9users.io). If I bind something to port 8081 I will not be able to access it from behind this corporate proxy.
I think you should add a spoof link option. Lets use the following example:
I bind nodejs to the defaul process.env.PORT.
I bind karma to port 8081
This would allow me to test and run applications on multiple ports and be able to access them from behind my firewall/proxy.