How to integrate beams and venting with drywall?
Interesting problem. If you've got metal vent, and a steel I-Beam, those will definitely move at different rates than drywall on wood framing. Sounds like you need something flexible for the transition. What about using self-adhering flexible membrane flashing material as (at least) part of the solution?  

I know you can get flex membrane flashing with a white surface, but I don't know if any manufacturers offer a paintable product.

Also, I'm not sure how to make a smooth transition from the membrane to drywall, but it might be possible with some careful mudding.  I haven't actually used membrane for this solution, but I am a big fan of the product for other purposes.  Here's a discussion article that mentions many types. 

Let us know what you end up doing?