Separate identities is to be able to create another identity for blocks. What I mean is to be able to create a copy of a block being used as something else in a plugin like in Sponge Energy where for example a furnace is a generator, when you activate is as it, and it generates power. Being able to create a separate identity would mean the generator is a “new” block but it just runs a different funtion as a generator. This could allow separate textures compatible with resorcepacks when the furnace is a generator it has a different texture since you don’t need the resourcepack to join, it downloads automatically and seems a more modded server then plugins. No forge mods needed. No needing to add blocks or new item ids. Just when the generator runs as the block and only then it takes the texture that is either included with the plugin or can be added with a resourcepack. This could make a new way for plugins to be made without forge mods. Just make a custom resourcepack and add it to your server and make a generator.
Thank you so much Sponge Energy! you gave me the inspiration for this idea here is the link to the Sponge plugin page:
It is simply impossible to add new block/item ids to the game without a forge mod. I should know - I tried xD. Anyway, it would be cool to see a system in which we could ‘track’ blocks and modify them to become special blocks, but that will probably be implemented through some fancy custom data, and not the official Sponge API. Sponge Energy does in fact use this custom data, but (unfortunately) there is no way, no matter how hacky it is, to get a vanilla client to recognize a new id - and load a texture for it.