I think that a key point of the new rule is this: installs "drop-in" precision trigger parts or other "drop-in parts" for the purpose of resale. The stress should be on for resale.

I think that this is a safety driven mandate, and in no way designed to discourage people from being gunsmiths. For instance, I buy a new gun. I buy performance parts, and have a gunsmith install them, no manufacturers license needed, as they aren't being installed "for the purpose of resale". On the otherhand, if a gunshop purchases a gun, then modifies it prior to placing it for sale, they would be considered the manufacturer. The only thing I can think this is intended to do is prevent a situation where a clueless noob (me) buys a hotted up gun with modifications not neccessarily intended by the original manufacturer.

Personally I think it is a solution to a non existant problem, but I think it is pretty far from a secret plot to make our guns paper weights.