Sneak peak of a mod I have been working on. It allows you to load worlds that were created with the old no longer used metadata values, which before 1.8 were sometimes used with Optifine and CTM to make alternate textures for blocks. With 1.8 the integer based metadata went away, at least on the surface. Underneath (for storage) it is still int based, and all the ints are the same. But int values that don't map to one of the standard block variations are rejected, and won't load in your world in 1.8 and up. Except with this mod :)

With this and Optifine, old creative worlds can be viewed again, as seen in the video above!

Also, a shot of the Conquest texture pack, illustrating what happens in 1.8 and above without this mod: