I feel an itch to address this further since this topic has been sprouting a lot lately.
What does open source really mean?
Any project could be open source, but what makes open source actually work is that the source code is made with being open in mind.
What does this mean in practice?
A closed source most likely does not contain as much helpful information, well-commented sections, tidy structures etc. Things one would expect from an open source project that a community could viably make use of.
Open source only works if the code is made to be understandable by a third party. If the Octatrack source would be released tomorrow, you would need to spend a ridiculous amount of time figuring it out.
Note that I am now solely writing about open vs. closed and what that means in a practical sense. There is also the aspect of intellectual property. There are implementations that the creators want to keep to themselves for various reasons.
Regarding JJOS - it is an anomaly. JJ did not reverse engineer the code - he had access to the source and was working at Akai during the development of the MPC1000. Hence, it was possible for him to make JJOS. This is not something one could do without having a) Source code b) Project knowledge c) Tools
These are [some of the] reasons why Elektron source code will not be made open source.
Will there be major feature additions to the Octatrack at this point (5 years since release)
Highly unlikely.
Has Elektron stopped supporting the product?
No.