Post effects would make certain visual effects (black and white, sepia, blur, glow, etc.) drastically simpler and more feasible (because they would run client side), and as such, it would be a pretty nice addition to BYOND. Would it be possible to add them? The only major limitations that I can think of is how some people still have ancient graphics cards and can't use shaders at all. Another issue, though, is that a lot of people won't be able to understand HLSL at all, because that's what BYOND's community is like.