This is what I think should be the penalty for an offender.
Revoke of any current contract, and even if negative service time. First offense, reduction of MLB service time to 3.00 years of service, and if under that service time subtraction of 1 year of service time. Second offense, reduction of MLB service time to 6.00 years of service, and if under that service time, subtraction of 3 years of service time. Third offense, Pete Rose.
For anyone that tests positive (and of course loses the appeal. To avoid any legit tainted supplements), suspension until WADA clears them that they are clean. And for those that get suspended, monitoring by WADA for second and third offenses. Which are much stricter than what MLB has in place now.