Actually, the Emerson ruling goes past that, I believe. IANAL, but the concept I have read is that of "strict scrutiny". Reasonableness, or being "rational", applies to all laws. They must be well-defined and must be crafted with the expectation that they accomplish a legitimate goal. "Strict scrutiny", however, is the criteria used to judge laws which affect rights. There is a burden on government to pass only legislation which addresses a "compelling interest" and the law must tread as lightly as possible on the right being infringed.
Emerson may yet get another day in court. The remand to the lower court means that Emerson will face trial. The trial judge will have to make decisions regarding the meaning of the law. Emerson will be able to challenge the details with regard to whether "strict scrutiny" will permit the law or not.
One area which will have to be covered are the circumstances under which Emerson regains his right to keep and bear arms. Where will the confiscated guns be? Who has the burden to care for them and return them to a person such as Emerson when he is no longer under a restraining order? To claim that this law treads lightly on the right to keep and bear arms but fails to protect Emerson's property, just because he "might" commit a crime while under a restraining order, is pretty hard for me to swallow.
If a person is imprisoned, then the government has an obligation to free him when his sentence is up. How is such an obligation carried out in cases like Emerson's. When does Emerson get a re-consideration of the restraining order so that he can have his guns back?
There are many hurdles yet to cross for the Lautenberg law and it may not, and should not, be able to cross them.