I am not aware of such a proposal, although England has a Mental Health Tribunal that deals with issues involve medical decisions made by a panel of judges including at least one legally trained judge and at least one judge with social work or clinical psychology or psychiatry experience.
In U.S. practice, the norm is to have these decisions made primarily by judges and juries who are informed by expert witness testimony offered by the parties (which is usually mandatory except in the clearest and most obvious of cases).
One exception to this rule is U.S. practice is that 72 hour hold orders that involuntarily commit someone to inpatient mental health care when that person is a threat to themselves or others can often be made by a suitably qualified medical professional (or by law enforcement) without obtaining a court order.
The basic problem with the proposal is that professionals with dual legal and medical training are vanishingly rare. I've never encountered a judge with that kind of qualification and I am aware of only a couple of privately practicing lawyers with those qualifications, anywhere in the U.S. over multiple decades. Dr. Joseph Ramos, for example, is a rare exception who proves the rule. And, any judge needs legal as well as medical knowledge.
Lots of legal cases involving mental and physical health (e.g. medical malpractice, termination of life support, mental health evaluations, guardianships, etc.), come up on a regular basis. See, e.g. the 2022 Annual Report from Colorado's state courts (breaking out annual case loads by case type). For example, Colorado has 1791 cases a year adjudicating incapacity for an adult in a civil case, alone, without considering insanity defense and competency issues in criminal cases, or medical malpractice cases, or involuntary commitment cases.
Certainly, there are far more such cases than all of the jointly trained medical and legal professionals available could handle managing even if everyone with these qualifications was employed full-time as as a judge doing so.