At times it bugs me that there's all that room right under the Castle but no way to make viable use of it; after the armory quest of course. I think it would be awesome for it to be turned into a functioning player home separated from the rest of the settlement. Whether this is done by merely cleaning it out and placing a workbench or a complete custom job like NV player home mods, but like so many other mod ideas it will likely have to wait for the GECK(at least for the latter version).