Heya Chris (I am assuming the name from your Username, do correct me if I am wrong)
Indeed, 8.5 is a major change to the architecture and took about 2 years to reach its Release Candidate stage. 8.1 is now totally unsupported so all resources linked to it including download links on other portals have been disabled.
The entire Virtual Assistant is a harmony of plugins and SIML working in sync. SIML is the interface all the plugins use to let users interact with functionalities provided by these plugins. Many, if not all, plugins use SIML adapters
to connect functions to commands.
All SIML files
by Synthetic Intelligence Network are released under Apache License so you are free to use them in any of your application(s).
A few of the plugins (including the major "Loader" plugin) used by Syn Virtual Assistant will be open sourced within a few days to let developers customize the plugins to suit their needs. We'll make an announcement in our social networks when we do so.
Teaching and learning part has been left solely on SIML. Developers can create their own Patterns to teach and save learned SIML Models to disk.
Syn Virtual Assistant is based on the Syn.VA Framework which is a platform and bot architecture independent library. So I particularly don't see any limitations in extending or creating a custom embedded Virtual Assistant using it.
What Syn Virtual Assistant does best is that it serves as a platform to integrate everything from VA Plugins, Bot interaction and display system, speech recognition, 3D Graphic Engine, GUI Plugin configuration and much more to assist in swift VA development rather than developers having to re-write everything from scratch.