Please bear in mind that Forge is a totally generic system built to handle CAD models from absolutely all design and modelling system seed files.
Therefore,only generic data is directly supported, e.g., geometry, properties and certain element relationships and hierarchies.
If you need specific BIM related information, you will almost certainly be better off accessing and extracting that using the Revit API.
It is extremely easy do combine data from any source in the world with the data made available by the Forge system, so there is nothing stopping you from combining the two approaches.
In fact, a number of the official Forge samples demonstrate that very approach, notably the Responsive Connected Database sample:
https://github.com/Autodesk-Forge/forge-rcdb.nodejs
I hope this helps.
Cheers,
Jeremy