Lots of people have speculated on the identify of SN. I have a few thoughts on it and thought to list it out here.
1. Working for corporation / government entity who would own the code. I believe SN, was a cryptographic / security expert who was working in a situation, where any work they were doing, would be contractually owned by a government or corporation. Eg. NSA, Federal reserve, Google etc.
FWIW – This is extremely common. People have day jobs and the work on their code projects in their spare time or even during working time.
2. SN is probably not Japanese. Or if Japanese, english was one of their native languages. If you are using a pseudonym online to remain anonymous, you are likely avoiding a demographic that you belong too… Just saying..
3. Probably not a group. The amble, discussions and request for comment / progress of the code was at a rate of development such that it was likely not a group. It would have taken too long for a group to coordinate and get back. Also you would have seen slightly different tones of voice or long delays and inconsistencies. Although they are quite open about their experiences. Mostly this is not a controversial idea.
4. They don’t need the money. The fact that they did not withdraw any money from their wallet (750,000 to 1,100,000 bitcoins) worth around 73 Billion USD at this time of writing, likely means both A: Don’t need or not doing it for the money and B: Are somewhat of an idealist (revealed in the comments SN made online about central banks / governments controlling currency). They haven’t touched one of the largest fortunes the world has ever amassed.
5. They are at minimum a top-level cybersecurity expert. Whether working for a financial institution or not, SN followed all the correct protocols to avoid detection and having their identity revealed. This all-the-while having an active digital presence and footprint. Eg. email address, registering a domain, publishing code and commenting on forums.
Mostly 2,3,4,5 are points that are non-controversial at this stage. I do believe strongly that 1. SN has not revealed his/her identity to date (and likely never) because their work would be owned under license from a government or corporation.