There's always the idea of having 2D text actually be 3D sprites, in which case the 3D-big-sprite-in-front-of-camera idea would work.
Alternatively, couldn't you also have a big animated image that you put in front of everything? It is animated so that different frames are different amounts of fading. It may not be as nice as alpha if done sloppily, but you could do it well, and it would also fade both 2D and 3D with one stone. Ha!
Alternatively, couldn't you also have a big animated image that you put in front of everything? It is animated so that different frames are different amounts of fading. It may not be as nice as alpha if done sloppily, but you could do it well, and it would also fade both 2D and 3D with one stone. Ha!