"Also, how will legalization affect employer drug testing?
Will card holders have any rights in this regard?"
Unfortunately I am not sure how legalization will impact drug testing–you would think that it should end discrimination against those with med recs, however, I don’t think that will be the case. This article goes over this topic: https://www.canorml.org/employment_rights_a_priority_for_Cal_NORML
Just goes to show that we still have a ton of work to do, even though cannabis is now legal in CA. I’d make a plug to support NORML. They do a ton of advocacy work for cannabis users in this respect.