The plaintiffs challenged §6001 as a violation of the Takings and Due Process Clauses of the Fifth Amendment. What seems to remain on appeal is the claim that the regulation effectively amounts to a regulatory taking (or its equivalent).
Again, oral argument took place on April 3, and no doubt the Fifth Circuit panel was waiting to see whether the Supreme Court might moot the case by declaring the entirety of the ACA unconstitutional. Now, one would expect the Fifth Circuit to issue its opinion in due course. (There have been no new docket entries since early April.)