Ooo, thanks for noticing the link was broken, looks like Epic’s changed to a URL with the asset name in it.
3D Widgets should be perfectly possible with the current system, there are a few functions that would need to be overridden in the BPC_Dialogue component. I haven’t attempted it myself yet, though I did build it with this possibility in mind (especially with the ‘passive’ dialogue I intend to use as chat-bubbles in my own game).
As for existing project integration, the dialogue system is non-intrusive for the most part. A dialogue ‘ScriptInterpreter’ actor needs to be spawned and maintained (variables copied across levels if desired), the dialogue components need to be placed on the actors who will have dialogue, and the Use system should be integrated or replaced with your own ‘use/interact’ system.
Hope that helps 