Wickard is not going to be overturned. We saw in Raich that even Scalia is willing to rely on it without questioning it, and only Thomas suggested reconsidering the whole aggregation principle and substantial effects test.
On the intrastate guns issue, we don't have a direct precedent because there are significant differences between an otherwise legal gun made in Montana and something covered by Wickard, Raich, or Stewart.
Wickard was not just innocently growing his own wheat, completely removed from any federal influence until the evil Supreme Court came along. He was a participant in a FEDERAL price control program. Congress was saying to farmers, "You can grow this many acres, and we'll guarantee you this much money per bushel." Wickard grew some EXTRA acres, beyond his allotment in the program to which he had agreed, and claimed they were for his family to use, and to feed his animals. Some of those animals were then sold (in or affecting interstate commerce.)
A homegrown gun maker who is not getting federal subsidies is not directly comparable.
In Raich and Stewart, Congress has decided to completely extinguish the interstate market in cannabis and in unregistered machine guns, respectively.
A homegrown gun maker who is not making NFA weapons is not directly comparable.