EFF was never intended to be used on the interface, hence it wasn't designed to handle streaming. Although it could be coded to stream it would be so horribly inefficient that it would hardly be worth the trouble. I worked on the EFF format with Lightspeed solely for use with in-game effects. So really, getting EFF working on the interface is something that it was specifically designed NOT to do.
The idea was always to create a new container format which could replace ANI on the interface. The new format would easily support everything that ANI does, but better. And it would be able to function equally well for effects as well as UI elements. This new format was never fully completed, but did have a basic working implementation when I started the Xt builds. The main missing piece was an app like AniBuilder which could be used to actually combine all of the animation frames into the container. However, the code got put in the back-burner, and unfortunately, it ended up getting lost along the way.