Allow new blocks to be added with datapacks

We currently rely on mods or convoluted and laggy methods like armour stands to add blocks, but it would be excellent if we could add custom blocks via datapacks. Downloadable maps would not need to rely on mods, nor would people be required to use third-party mods just to add a few blocks.

A block's .json file would have the typical block info: shape (normal, stair, wall, flower, etc), blast resistance, luminence, waterloggable, and so on, plus a direction to either an included texture or a vanilla texture.

These blocks would be mostly decorative while keeping with the existing shapes -- no vertical slabs! -- to greatly expand on the visual variety and decorative nature of Minecraft. This would also leave you free to add blocks in future updates with gameplay changes. 

We can already change so much with datapacks including adding biomes and world generation. Adding custom blocks would be a step in the right direction.