It depends what you mean by 0-level. I've seen different interpretations over the years.
If you mean (and your example of a wizard with just a cantrip suggests this) a class level that's within the class but weaker than Level 1 - then really you're just asking "Should level 1 be much weaker?" Whether you call that first level 0, 1, X or Orange is immaterial.
If you mean that the class has not yet been chosen, and that the player chooses a class upon progressing to 1st level - sure, it could be an option, I guess. Why not? I wouldn't want that as default, but it could be fun to do occasionally in the right campaign.