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 asked the court to overturn the Slaughter-House Cases, 83 U.S. 36 (1873). 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 it had been overturned, the Selective Incorporation process may have become unnecessary, since the entire Bill of Rights, including the 2nd Amendment, would arguably be applied to the states.
In attempting to overturn Slaughter-House, this case garnered the attention and support of both conservative and liberal legal scholars interested in its potential application in areas outside of firearms law. Their interest was that if Slaughter-House had been overturned, it would have been possible 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 have been applied against the states automatically.
In his concurring opinion, Justice Thomas alone supported overturning the Slaughter-House and Cruikshank decisions,[15] proposing that "the right to keep and bear arms is a privilege of American citizenship that applies to the States through the Fourteenth Amendments Privileges or Immunities Clause."[16]
https://en.wikipedia.org/wiki/McDonald_v._City_of_Chicago