I was able to successfully install the Developer Edition following the provided guide: https://docs.shopware.com/en/shopware-platform-dev-en/getting-started/installation-guide
However I would like to test out some of the Features provided by the Professional Edition, how could one install the Professional Edition in June 2019? Will this only be availabe starting with Q3 in July 2019?
There will be an installer like you know it from shopware 5. The extra functionalities will be provided via plugin, as soon as they are available. Please have a look at our roadmap to get a detailled overview of when those features will be completed: https://www.shopware.com/de/roadmap/
There won’t be any difference between CE / PE in july (apart from official support) - this will be added as soon as those features are ready during Q3.