User Penney16 on August 11th, 2019 figured out how to finally export rigged models for BfBB from 3DS Max. This is a short guide on how to do this.
How To Export Rigged Models From 3DS Max
In order to export rigged models, you need to follow these steps. First, open up 3DS Max and import your model of your choice.
Now, once you've done what you want to your model, in order for it to export rigged, do this very important step. select ONLY THE SKELETON (bones) AND LEAVE THE OBJECT(S) UNSELECTED! If you select all, or just the object, it will NOT export rigged! Once you've selected only the bones, click export, and export with the recommended DFF export settings, and once it's exported, re-import it back into 3DS Max to check for rigging. It should have exported rigged, and if so, it should work in-game! If you need a visual tutorial on this, it can be found Here