The pro-RKBA judges will have nothing substantive (but weight) to contribute to the case, and actually have no reason to grant cert because, strictly speaking, they have nothing to add.
The anti-RKBA judges are actually the ones more likely to grant cert precisely because they don't like the current verdict.
Fenty had to appeal.
I predict SCOTUS will not accept the case. Really, they have nothing to add.
I believe you are correct. Since DC comes under the control of Fedral legislation and is not considered a state, it is possible to repeal this law without making any comment on the individual right issue for the rest of the country.