good reason = improvement of Bitcoin
Improvement of Bitcoin source code is one of good reasons, I agree.
However, it does not mean satoshi has to appear in public in order to contribute to Bitcoin source code. satoshi can make such contribution in a shadow and it's thanks to a real decentralization of Bitcoin, isn't it?
satoshi decided to leave our community but he did realize that there are different ways to contribute to Bitcoin.
Sum up, no good reasons to appear again in public.
The improvement in bitcoin is really now a serious and very compelling reason for the possible appearance of Satoshi Nakamoto due to the fact that individual groups still cannot agree on how they see his future. This is not even necessary in order to say how to improve bitcoin, but at least in order to decide with your authority the question in which direction to improve it. However, we understand that Satoshi Nakamoto will never reveal himself, because he deliberately hid his identity from the public and quite a long time has passed.