All of the post-Heller cases, including McDonald, NRA v. Chicago, Nordyke and Maloney, have argued that the Second Amendment, in addition applying to federal jurisdictions, should also be applied against state and local governments, using a judicial process called Selective Incorporation. Selective Incorporation involves convincing the court that a right is "fundamental" by being “implicit in the concept of ordered liberty” or “deeply rooted in our nation’s history and traditions” as defined most recently in the 1968 Supreme Court case Duncan v. Louisiana.
In addition to claiming the Second Amendment should be incorporated through the selective incorporation process, McDonald is unique among post-Heller gun cases in that it is asking the court to overturn the 1873 Slaughter-House Cases. Slaughter-House determined that the 14th Amendment's Privileges or Immunities Clause did not apply the Bill of Rights to the actions of states (and by extension, local governments). If overturned, the Selective Incorporation process would be moot and unnecessary, as the entire Bill of Rights, including the 2nd Amendment, would be applied against the states.
In attempting to overturn Slaughter-House, this case has garnered the attention and support of liberal legal scholars interested in its potential application in areas outside of firearms law.  If Slaughter-House is overturned, it is likely that constitutional guarantees such as the right to a jury in civil cases, right to a grand jury in felony cases, and other parts of the Bill of Rights, as well as future court rulings and existing federal precedent, not universally guaranteed in actions by the states would be applied against the states automatically.