One of the Scribus devs, Craig, has started to upload OSX nighty EXEs for the community to test. They live on SourceForge: https://sourceforge.net/projects/scribus/files/scribus-svn/1.5.3.svn/
There is a 32bit and 64bit version for you to choose from.
- These are considered 'unstable'
- Obligatory: Scribus team takes no responsibility for any data loss. Use this at your own risk
- You can run different versions of Scribus simultaneously on Windows
- Backup you work before you open it in 1.5.3svn, it isn't backward compatible
- If you're helping to test bugs, if you report a bug please mention what nightly version you installed and OSX version