It is a good idea to detect encoding when opening a file. That should stay like that.
However, when creating a new file, it would be nice if it defaulted to utf-8.
When creating a new file in Leafpad in Parted Magic, it defaults to utf-8. I don't know whether you have time to check out how it is done in Parted Magic.
This is not high priority. However, if you have it in your mind, and at some time in the future you update Leafpad, you may have the opportunity. It is not essential, but would be nice.