I'd also like to see this added in, and i also only like using Forge as an API, too much work for players to add a list of APIs. That's why i was happy to see it dropping dependencies.
Will there be a hook for creative tabs? Also, I think a hook for creating new custom particle effects with custom textures be nice. Just a suggestion. And since 1.3 is technically SinglePlayer and MultiPlayer merged. Would mods be MultiPlayer compatible automatically, or would we still need to wait until 1.4?