Thanks for the nice essay. Play is an important aspect of innovation as you rightly point out. We all seem to know what play is, especially when children play, but what play is for adults is one of those kinds of words. Like defining what a game is, play is something that we seem to know, but then cannot really generalize.
What is the difference between play and work? Oh, work is not fun...but then what if work is fun? Is it play or is it work? Some people say that what they do for work is fun and some people say what they do for work is not fun.
The essence of your essay really is that a childlike approach to exploring the world can help us better understand that world. I daresay that I would even push it further and say that the way that we learn before we reach consciousness at 6-7, by play, is just as important as the way we learn after consciousness and the more structured play as we grow older.
You use the word fun a lot in your descriptions of play since what is fun is usually an indication of what is play. However, some people have fun doing things that bore others to tears, and so the actions are not really the key. It is the desire and motivations that are the key.
Implicit in your essay are desirability and motivation. It is by imagining futures that are desirable that we decide what is fun and what is play. But hunger and fear are also important determinants for predicting desirable futures. For science, curiosity is a much more important driver than fun or play, for example.
Is curiosity about how the world works fun? I think so, but most people that I meet simply do not have much curiosity about how the world works. Instead, their curiosity is channeled into movies and books and UFOs and ancient aliens and so on. Is that fun misguided?
And finally, what about playful behavior that injures others or damages property? Play is a useful allegory for a desirable future, but it does have its limitations. Like all behavior, play can be constructive and enlightening and play can also be destructive and abusive of others. Your doctrine of play should also address the dark side of human play.