Tradition has it that he or she is crowned king or queen for the day!

Yes, Danielle, your version is a higher register of English as it uses the (almost extinct) subjunctive. It is still commonly used in sentences like "Long live the king!" This is an exact parallelism to "The tradition is that he be crowned." instead of "....he is crowned" (which would be the indicative and not the subjunctive mood).

Bonjour Danielle,

Couronner is a transitive verb so takes a direct object. I see "he or she crowned (couronner)" as being valid.

Your proposal would introduce the verb être before couronné (past participle)?

I don't see this construction (passive voice?) as appropriate.

Let's see what others may comment.

Bonne journée

Jim