I think that Mr. Madison (and those who shared his views on the matter) would simply have said, "The right of the People to keep and bear arms shall not be infringed", were it not for the need to appease the landed gentry, and the other would-be aristocrats, who might have seen an armed citizenry as a threat to their wealth and power. Adding that unfortunate dependent clause about the "militia" was, IMO, designed to assuage the fears of the slaveholders and the mercantile class.
I don't think that's the issue. I think it more likely that Madison et al. would have feared that, without such language, the RKBA might be interpreted as only applying to a small subset of weapons, excluding some that would be necessary for effective military use.
It is left deliberately vague to give us more power, but at the same time to clearly discourage a single armed citizen from offing a government official who may tick him off. At the same, same time. a single American citizen is allowed to take armed action against armed individuals who threaten him, his life, or his family's safety, who may of course be working for the government, for instance, policemen who raid the wrong house (A purely hypothetical case) .