Adding infinite amount of new blocks

Suggestion and some questions:

It would be cool to be able to add infinite amount of new blocks/items using Sponge (for vanilla clients, in conjunction with resource packs).

Would it be possible in any way to register these new blocks/items without replacing old ones? It would be a very useful feature.

I have very little understanding how this stuff works but I thought it could be worth it to suggest this.

With 1.7 and before, you could cheat and use resource packs + block metadata, but I believe that is no longer possible starting with 1.8.

Without players also having a client mod, it’s not possible to add new blocks until Mojang’s own API comes out.

That is too bad.

I have used the extra metadata in some occasions to make new items. I guess I won’t be updating to 1.8 any time soon if that is no longer possible. It would break a lot of stuff.