Or make it the only issue to appeal. I don't expect it would be decided be our state supreme court, but it raises an issue of due process for the federal courts. I have been principally engaged in child support issues and litigation involving a little known family protection provision in the Social Security Act (42 U.S.C. 1301(d)), in addition to a federal action to strike down Minnesota's Battered Women's Act (see my web site). A few here have raised the fathers natural right to guardianship argument in various pleadings, but we have not yet made a focussed argument. It would be best to find someone who has just been served a petition for divorce to challenge the courts taking jurisdiction of a custody issue without a parental fitness hearing and decision. That could tie up everything, or give pause for the petitioner's reconsideration, which is the whole point.
I have a great deal of research done on older decisions that affirmed this position, and the history of decisions that gradually made it look like the "best interest" review was required (under probate authority) rather than "grave and weighty" reasons for interfering with a father's natural rights. The cases cited became those that found the father's unfitness, or some danger to the child were it to be left in his care. The rest seems to be due to uneducated lawyers, or an intentional perversion of the process. It is, however, still the law.