in opinion, based on all mass produced products in the world quality would eventually go down on mass produced cannabis. think about it farms of cannabis would be much like farms of everything else, they cant use clones on 50 acres of land, and weeding out males would be a huge task. it would probably be harvested with commercial machinery, and de-stemmed and de-seeded also using commercial machinery. everything else would probably be immediately ground and dried then pre-rolled and filtered. then sold in packs of twenty just like cigarettes. so it would probably be similar to swag if you ask me.
that said like fine wine there will always be a demand for connoisseur grade bud. individual companies will thrive selling high grade cannabis at competing prices.
if you walk into a cali dispensary you will not find any mass produced pot. all of there product is somewhat local (everything is grown in california) on a federal level you will have companies similar to alcohol and cigarette brands supplying people accross the nation with identical (or as consistant as possible) marijuana.
but that wont be for quite some time even if the bill is legalized. all this amazing bill does is stop federal regulation except for accross state lines. the people in medical marijuana states will be ecstatic at the fact that they no longer have to worry about dea raids on there favorite dispensary. with this bill marijuana industries will finally be able to move out of the dark. no matter what the state says every dispensary is breaking federal law at the moment and lives with constant fear of being sent to jail.
this bill puts marijuana regulation back in the states hands. for those who do not have medical marijuana or decriminalized marijuana they are still in the same boat as before.
still this is a huge step forward and is the best first step for making marijuana legal across the USA, and eventually the globe.
as for additives. maybe one day. but i don't see the current generation standing for any additives in there bud. i wouldn't, especially since i can grow my own. although there already are plenty of things added to bud as it is. ive seen bud that had fabuloso (a mexican cleaning product), amonia, urine, pesticides, bud mold, insect carcases, powdery mildew, webs, insect nest, and even a human finger! all of/ most of these in sacks purchased in non-legal areas, so legalization may actually stop additives in bud, except pesticides and cultural problems that people try to sell as safe bud anyways