I have not found any more detailed information than what is written in the press release:
"The fourth software update released in the beginning of March, raising the software to commercial readiness, will again include many important improvements and new features. These will include further improved performance, extended landscape support, lots of visual improvements, lots of new camera functionalities, enhancements to the Jolla store, new general settings, and many more."

For me the current DEALBREAKER is the lack of native offline mapping.