We will provide more details about the way that will work soon.' You will, however, be able to recreate much of this content using our homebrew system for private use, and we will occasionally provide public homebrew instances of the highly-popular archived content for your convenience. For all previous playtest content, it is either available already in a published source or it is considered 'archived' and will not be available in the official UA source here on DDB.
'We will integrate all appropriate Unearthed Arcana content from January 2018 going forward into D&D Beyond. If you follow along with the links the mods shared you'll get your answers, but to save you some time, please refer to this. Monstrous Compendium Volume One: Spelljammer Creatures