Having the option to work with libraries that require API keys would be a neat feature if they included the option for the user to setup private environment variables to run the script. The general thought being that the variables would remain secluded to just the user entering them and they would be unsharable items, preferably encrypted values until the end user runs their own code.

If a repl has associated environment variables, other users who attempt to run the code would be required to enter their own API keys prior to execution. Not sure if repl.it wants to take on the responsibility of encrypting sensitive API keys, but this would be a very useful feature if it could be done securely enough.