And i have never seen a java game with shaders :/
As has been said before - it's not Java doing the 3D. He's using a special library to access OpenGL, and yes, it supports shaders.
Don't forget this is Java, with a huge overhead for function calls (all are virtual and non-inlined)
Java can and does actually inline functions when it thinks it can. Just because you can't declare it explicitly doesn't mean the functionality doesn't exist. Yes, Java hides a lot of optimization details, however that does not mean the JVM is not aware of them. The latest JVMs are very good at optimization.
Bump mapping would be very slow with the sheer number of lights that could exist.
I'm thinking that that could be overcome somewhat by prioritizing lights at the user's location and only using, say, the top two or top four lights for the bump maps. Generally speaking, people aren't gonna notice much if lights further away aren't contributing to the maps. There's not enough depth in most bump maps to make people aware of missing lights.
Can it be done, and how would you other Minecraftians feel about this addition to the graphics, would it be a nuisance?
There are two basic ways to create motion blur - the realistic way (multiple renders between frames), and the fast way (overlay previous frames on current frame). The fast way can be a cool effect, but tends to exaggerate the blur unrealistically. The realistic way looks realistic, but since you're just rendering the frames multiple times, it will obviously affect the framerate.
All that being said, my opinion:
I personally would like to see the graphics improved. Yes, the current style is very retro, but I think that sometimes getting stuck on one way of doing things can hold back the potential of a game.
I think the graphics can still be stylized yet take advantage of modern hardware - look at TF2, Darwinia, and WoW: Cataclysm.
All are using some shaders for their graphics, yet they very much retain a very recognizable, stylized, and even retro look. No, shaders will not kill the look of a game if done carefully.
I think people are a bit too stuck on the idea that shaders == realism. That is certainly not the case, as they can add unrealistic but fun style to a game.
. . . and I don't really think that I'd like to see this game stick with a flat illumination model. As retro as it looks, I really don't think it really has to be that
retro. I'd like to see what something like ambient occlusion or some other fast global illumination shader would do to this game.
I've been playing around with some of the texture packs - and I don't think that adding some detail is really gonna hurt Minecraft all that much. It's still the same game, and it still plays the same way.
The game doesn't look bad at all with different graphics, and I think people are just fearing change.