In some occupations that might be OK, but I don’t understand how that would work in occupations where there is a public interest in ensuring the competency of the people who are involved. If someone is going to build a 25-story building in your neighborhood, I think everyone can agree that there’s a legitimate interest in having it designed and constructed by licensed professionals.
Charles Murray suggested retaining the current licensing process, but making it merely an option for someone who wants to practice a trade. People who get licenses could say that to potential customers, and people who don't couldn't. That way we eliminate the cartel problem of licensing, while retaining its alleged quality-enhancing effects.
It would be interesting to see how much customers value obtaining a license. Maybe a lot, maybe not so much.