Ideas for the future of Siril are stored in the issues tracking system and can be seen by version in the milestones page. The list of known bugs is mixed with it and the full list is available here. The complete changelog is available either in the list of closed bugs or in the code source commits. A summary is available in the news section above and in the page of each release, as well as in the ChangeLog file. If you want to contribute, you are welcome!