The HTML Export plugin supports automation API (can be called programmatically). This allows you to execute export with code. The addin can be used from any language that supports automation, including in particular Visio's VBA, .NET languages, powershell, etc. Basically, if you can call Visio API, you should be also able to call the plugin API. The type library is installed with the addin (named is called "GenerateVisioSvg"), and you can use it to add a reference to your project for autocomplete.
With API, you can:
- Export to disk, sharepoint, github
- Get/Set any export parameters (paths, options, authorizations, etc)
The documentation refers to the latest version 1.2