Sure it would be great to have a way to plug our own shaders into the engine but I imagine that would be client-side anyways if at all achievable.
Well, shaders are a part of the rendering, and thus would be clientside, yes. The acid trip shader shown above deforms vertex positions but the objects aren't at all altered; assuming we can put our own GLSL shaders in at all, that would be possible. And hilarious.
If we can turn specific shaders on and off at runtime,
commandtoclient('getrealhigh') will be happening. I guarantee it.