The biggest difference being that it’s a forge mod itself. Other than that, I suspect it’ll be responsible for the same sort of features, adding or modifying non-vanilla server-side functionality. Also hoping that, due to it’s association with Forge, it’ll offer some hooks into client/server mods as well (which I guess isn’t necessary, but could be nice, possibly).
It won’t use the same method names, or even be structures as Bukkit for the most part. If you haven’t already seen it, and was/are a Bukkit developer, here’s a thread to look at to kinda show ya how the starting of a plugin will be different.
It serves a similar function as CraftBukkit, but is being written from the ground up, if any of that helps. As far as I can tell, they’re not looking to reflect any code from CraftBukkit, but only to provide similar, and quite possibly better, functions than it.