The plug-in system is there for anyone to use to create plug-ins. You can run a plug-in on testnet without an Armory signature.

We currently have no plans to develop any plug-ins for the public version of Armory, but we may do that in the future.

If someone were to present us with a completed plug-in that would be useful for regular Armory users we would consider reviewing the code and possibly signing the source so that it will work with our signed releases.