I am ready to place my bet if there are any takers:
SCOTUS will say:
1. The 2nd amendment is an individual right
2. The right apples to everyone- not just people in a "militia"
3. DC ban is unconstitutional because it constituted a total ban on firearms. Congress is allowed to enact legislation to regulate firearms, however, it must have the "burden of proof" that such a firearm interferes with the rights of others (by being excessively dangerous...) and it must specifically describe the regulated firearms in detail. The laws it writes must go under careful future judicial review to ensure their constitutionality.
4. Since DC is not a state they will only cover federal laws. They will not address if the 2nd amendment prevents States from writing their own firearms legislation. (they already said this when they took the case)
This is not going to cause any big changes in the law immediately (except for DC), but will open the door for future cases in the coming years. Let the battle begin!