This issue hasn't really been tested, and it's unlikely to be because the parties who would likely end up in court would have the option of estoppel. This is just theoretical, I don't think it would work in a real case, licences like these are so commonplace. But it would be nice if there were some certainty.

It'd be nicer if we didn't have to rely on estoppel, is anyone campaigning to have dedications to the public formally recognised by the law?

I wonder if these licences can be revoked after they have been dedicated to the public domain. If they are just bare licences then they can, they would have to be contractual licences to avoid that, but is there enough consideration in this agreement?

I doubt this would mean anything in reality, courts would find a way around this, but in theory these licences could be revoked at will by the copyright owner (with sufficient notice).

except that originality (creativity) has a different meaning in copyright law to the everyday notion of originality. Copyright law is used to protect unfair competition in Australia, "originality" includes the skill and labour used to create a work. This interpretation of "originality" dates back to a case in 1900 (Walter v Lane). I personally don't like the use of copyright to police unfair competition, but that's just how copyright works (in Australia at least).