In this stage, Joomla team focuses on 3 main features and they will be completed in the Beta release.
Backend Template Redesign
Approx: 70% done.
Joomla 4 implements a new proposal in backend interface. There is a lot of work to be done to fully meet the requirements of the invision prototype.
Approx: 95% done.
com_content is almost migrated, there is only a pr not merged yet which turns the router access into a service. The rest of the core extensions will then be done step by step.
Approx: 10% done.
Prepared statements have been implemented to the Joomla 4 database library in order to increase security in the code base. PostgreSQL users are welcomed to help test the PDO library that will be implemented in Joomla 3.9
Note: SmartAddons' Joomla templates can work with this latest Joomla release. You can update them to Joomla 3.8.x and follow this article for Fix Bugs, Errors When Update Sj Templates to Joomla 3.8 for bugs fixing or contact us here, we will help you.