All of that will be forecasted by many people more savvy on the law than myself, so instead, I’m going to look very far ahead into the future: what if Section 3 is struck down for good?
Section 3 of the Defense of Marriage Act is the section that defines marriage, for the purposes of the federal government, as an institution between one man and one woman. Here’s an excerpt (which is almost the entire section; it’s a very short law):
In determining the meaning of any Act of Congress, or of any ruling, regulation, or interpretation of the various administrative bureaus and agencies of the United States, the word `marriage' means only a legal union between one man and one woman as husband and wife, and the word `spouse' refers only to a person of the opposite sex who is a husband or a wife.
There are over 1,000 federal laws relating to marriages and spouses (social security, veterans benefits, tax laws, etc.), so this is the biggest part of the law. If Section 3 is struck down (or, less likely, repealed by Congress first), then couples who are legally-married in the states (plus DC) which allow it will technically be treated equally under federal law: they will be eligible for the 1,000+ rights that straight couples are currently entitled to.
But that’s not the only section of the bill. Section 1 just concerns the title, so that doesn’t have any real legal implications, but Section 2 would still be standing. Section 2 is the section allowing other states not to recognize gay marriages performed in the states that allow them:
No State, territory, or possession of the United States, or Indian tribe, shall be required to give effect to any public act, record, or judicial proceeding of any other State, territory, possession, or tribe respecting a relationship between persons of the same sex that is treated as a marriage under the laws of such other State, territory, possession, or tribe, or a right or claim arising from such relationship.
Because of this section, any state is allowed to say that a couple married legally in, for instance, Connecticut, is not legally married in their state. So while eliminating Section 3 will go a long way in procuring equal rights for legally-wedded gay couples, those couples are still only limited, in terms of rights endowed by the state (such as getting a divorce, state taxes, or adoption laws), to the states that perform and recognize gay marriage. Essentially, we will not have full marriage equality nationwide until Section 2 is eliminated as well.
(Side note: That will probably be argued on the basis of the Full Faith and Credit Clause (Article IV, Section I of the US Constitution), which states that "Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State." That seems to contradict the idea that one state does not have to recognize other states' marriage laws. Again, this is coming from someone who only has a college student's understanding of the law.)
What I want people to know is that this DOJ announcement does not cover all of DOMA, and even if Section 3 were eliminated today, we’re still not at full marriage equality – we won’t be there until every single state recognizes and provides gay marriage. The DOJ’s announcement is a good thing, there is no doubt. But it is only one additional step on a road that will require a much longer journey.