I don't want the shaders. Just because it looks nice doesn't mean its absolutely essential to a game. Without terrain/interiors the game would loose it's "shine," if you will, for many people. The main focus of Blockland is building, which is the only reason I can think of for having this, to force the way you play the game. Instead of being able to build where ever you want from maps such as Emerald Isle 4, Slate Paradise, or The Wastes, just to name a few, you would have to build on a flat, never changing surface that just gets boring have looking at it for a few seconds.
Most servers these days don't have anything to do with serious building and rely mostly on terrain/interior maps and span over a great length of the map. Having to build all of that terrain and making it look good would take forever and the player can't get from point A to point B smoothly unless you use ramps, which would make the terrain look ugly, or you use 1x bricks which would just take to long. Terrain/interiors also add a mood from the textures and lighting, something not achievable with bricks.
One thing I love about terrain is finding a hill, putting some cubes down, and building a base. Without terrain one would have to first build the hill and make sure there is room enough for the floor for the base. Then they would build the base. This just adds an unneeded step and many people aren't good with terrain, but great with stuff like exterior. The outside of a build, like the terrain, adds as much to a build as the interior and being unable to build terrain outside of the build would make most builds just look ugly.
I understand that the terrain and interiors can't cast shadows, but can't we at least have just bricks casting shadows while still having terrain/interiors not cast shadows? It might not look the great, but for an option that you can just turn off anyway I think it would be good enough, at least until they can figure out a way to make terrains/interiors cast shadows or have some sort of public brick terrain generation.