All of these would work, I think.
Some of them actually did commission research for just that in the 1970s but it doesn't appear to have been anything to be considered seriously back in those days, at least.
Erm....only if marijuana cigs were to be packaged as tobacco is today. Otherwise, not even close, especially if kept as pure as possible.
I think you'll see most of the cigarette makers take a swing at it -- RJ Reynolds and Philip Morris or Altria or whatever it's called would definitely go in. They'd have a huge advantage over the rest of the pack on distribution infrastructure -- they have working relationships with everyone from WalMart to Ma's Rural Crossroads General Store.
They probably can't switch a production line from tobacco to marijuana immediately, but I suspect they'd have a read on the situation enough that they'll have a good bit of head time before they have to go online, enough that they should be ready to roll once it goes legal.
That might be doable in today's climate, with the right moves taken. But there is yet another problem: what if they adulterate the product so much that people who smoked "pure" weed won't even touch the stuff? That presents a huge problem, especially with OTL's cannabis culture.
That was something I thought of, but more from the perception perspective. The cigarette manufacturers have massive PR headaches for obvious reasons, and that's going to make them an exceptionally hard sell to current users -- many of whom I'm willing to wager veer to the left and are not huge fans of their tactics. Most current users would probably stay with what they know, either growing it themselves or getting it from their go-to dealer.
RJR and PM would have to cultivate new users -- people who might be willing to try it but don't want to break the law, or don't trust the product as it's peddled now, or who are just flat curious. They'll have to market and market hard, but that's never been their problem.
The only way they can get a share of the current users is if they can get the price down to the point where users are willing to sacrifice purity/morality issues for a cheaper high.