Why exactly SHOULD he turn of the cameras if he is just experimenting? You're just inventing these weird rules for people. Have you considered people enjoy watching his coding without any idea what the end result will be?
Because by living in the public and being a well known person you are inviting expectations. If you don't want to continually let people down because you don't like the pressure of finishing things then don't let them down. You can't have your cake and eat it to. You can't say "here's this cool thing I'm working on, watch me work 24/7" and "bored with this, sorry".
What... what weird obsession is this? You continue inventing requirements for this particular person out of thin air. Try to understand that there is absolutely no reasonable requirement, whatsoever, for Notch to continue doing some pet-project that he has publicly started. None! Just because he is a well known person does not truly remove any of his normal rights to decide what to do with his spare time.
Why shouldn't he stream? notch is a famous and well-known developer that many people look up to and want to learn from. What is the problem with letting people see his workflow when experimenting with something new?
His stream is a big deal watched by a heck of a lot of people. If he just wants to experiment he should turn the cameras off like most of us do.