This decision will be as narrow as the cert described. Answering the question that was presented and dealing only with that question. Does the District of Columbia have the right to ban an entire class of weapons. Specifically handguns.
SCOTUS of the last several decades have been very loathe to issue broad rulings. This SCOTUS is no exception.
I would love to be able to install a happy switch on my ARs with this forthcoming ruling. It won’t happen, as you pointed out. They will only answer the question posed. Another case (or several) will have to brought forward to address the rest.