Right, so we all thought "No... it won't ever work! NEVAAAAAA!" But that's wrong.
I've managed to get the Realism Pack to work in the web browser! Unfortunately, java code signing deems it won't work.
If any of you happen to use Icedtea as alternative to Java, http://technomagic.net/mods/realism/ is where you can use it (feel free to ask me to add more mods - suggestions always welcome). But, if using Java, I'm afraid you'll be met with some java security errors and the lot.
And I would rather not have to do this -> <sim9> You would have to learn about java code signing. It's not easy.
Sim's Comment:
<sim9> neat
So... yeah. Theory broken, texture packs do work in browser if you figure out how to set it up and happen to use Icedtea, instead of the overruling Java.
Image to prove myself honest: