I believe Simon has been working on adding instancing support to Visionaire. He's just added in a visual scripting system, & a whole new custom scripting language based on C#, & box 2D physics engine, so to be completely honest, I have no clue what's actually possible currently.
Visionaire was originally created with point & click adventure games in mind, but the new features are to make the engine much more flexible. Only Simon, can really tell you whether or not it's possible to create an RTS/building type game with Visionaire & if possible, then how difficult/easy it will be. I personally live behind the motto that anything is possible when it comes to VS - I'm always trying to do things that weren't intended by the engine, because it can be a fun challenge.
In regards to the online side of the engine, VS has support for Lua socket & cURL, but I've not actually tried using either of them, so I don't have a clue what's possible to achieve with them.
Also feel free to join our discord server, if you want. You will likely get a much faster response on there. @ https://discord.gg/g5zFejW