We all know that this will be resisted on a religious liberty basis. I don’t know how elaborate it is to ‘register’ as a Christian Scientist. Perhaps, Christian Scientists will make a killing selling memeberships to those wishing to join their group.
I have seen that a memebership in a so-called ‘Christian Ministry’ plan could qualify as an opt out.
The bottom line is that opting out of 0-care would probably result in an IRS audit which could be worse than buying the insurance in the first place.
As far as I know (I spent last 15 minutes reading on the Internet about that) the membership is free, and the yearly dues are "at least $1" - which was some money 100 years ago, I guess, but today you can collect $1 from the ground if you just walk around the block.
The biggest stumbling block for many would be in some incompatibility of Christian Science with other Christian denominations. I quickly read some critique; some of it is pretty harsh. The membership form requires you to break your ties with the other denomination.
If one wants to join CS and is not otherwise engaged she only needs to find two members to sign her application. Those members are supposed to ascertain applicant's beliefs. I do not know how hard it is to pass that test. I think anyone familiar with basics of Christianity would pass easily. You can't be expected to be an expert.