Hey Tobias,
No, we have no plans to make a sandbox environment for LimeLM. Historically when companies make sandbox environments they quickly get out-of-sync with the “real” version, and begin to have their own divergent behaviors (making them functionally useless as a development environment).
I'd recommend creating a separate user in LimeLM with restricted access (say, the ability to create keys, but not remove them), and have the test environment be a separate product and version. Then, whenever you need to “clear out” these test keys, you can have a user with the appropriate permissions do that.
Does that make sense?