Release date :
The date is shifted from 27th Nov 2018,, in order to give more time for RC testing. Final date of release is not yet announced at the time of writing this information.
Testing :
In case you want to test, you can use this plugin WordPress Beta Tester. Don’t forget to take backup before installing the same.
The final known PHP 7.3 compatibility issue has been fixed. You can brush up on what you need to know about PHP 7.3 and WordPress by checking out the developer note on the Make WordPress Core blog.
Twenty Nineteen
Work on making Twenty Nineteen ready for prime time continues on its GitHub repository.
This update includes a host of tweaks and bug fixes, including:
Add .button class support.
Fix editor font-weights for headings.
Improve support for sticky toolbars in the editor.
Improve text-selection custom colors for better contrast and legibility.
Fix editor to prevent Gutenberg’s meta boxes area from overlapping the content.
What to do ?
1) For existing websites : Create a development environment and test it with WP 5, if everything looks good, update your live site
2) For new sites :
a) Check for theme/ plugins are compatible with WP 5 or not
If you face any difficulty, you can go with WP 4 itself and once WP 5 is stable upgrade your site.