No support. Some shaders have a serious impact on people's FPS. (Yes, I'm talking about the Super SS)
Plus, that would essentially be editing a players personal settings. Servers have never HAD that ability, or they could basically change your CONTROLS around.
Anything you do with command blocks can really mess with your FPS, so that is invalid.
Servers have been able to control what texture/resource pack you have for quit a bit of time. If you go to Hypixel and play the Blocking Dead mini game you have to use their resource pack that changes a few items and blocks. Then when you leave the mini game it goes to your original pack. Thus that point is also not valid.
I support this, it could be used for some cool FXs and RPGs.
97% of teenagers would cry if they saw Justin Bieber on top of a tower about to jump. If your the 3% who is sitting there with popcorn screaming "DO A BACKFLIP", copy and paste this as your signature[/b]