The ACA could potentially be overturned completely by the Supreme Court, and a ruling on the case may not be made until June 2021. If it's overturned, then all those subsidies, Medicaid Expansion, and everything else that's part of the ACA will end, but it may not be completely eliminated until 2022. No one knows what SCOTUS will decide, but the odds aren't as favorable for the ACA with the new make-up of the court with a new justice as they were when RBG was in the mix. But, it could go either way, or they may just strike down the mandate leaving the rest of the law in place.
Also, ACA uses MAGI for the PCT/CSR calculation, which can differ from AGI, such as for SS recipients.