X-ray using block models

I don't see how this could get fixed, and the player can anyway use some mod to use xray. It's a pain for servers alright, but for adventure maps or solo I think the players are only ruining their own experience when using xray.

Only "fix" I know is what several plugins do on servers: hide all the blocks (do not send them at all to the client) which are not supposed to be seen. I don't think Mojang wants to do that, even if it was disabled by default.