So what part of F:NV is officially cannon? Things like killing Ceasar can't be, IMO.

Sorry for the vague thread. Can't think of how else to word it.

http://farm9.staticflickr.com/8022/7528121270_549c5b4426_b.jpg

And we don't know.

We don't really know what official details will be. Bethesda may mention a small detail in Fallout 4, as a rumour. It might be "Did you hear about that big battle over a dam way out west?" Other then that, Bethesda likely won't tell us the canonical ending in Fallout 4. Bethesda doesn't like making one ending canonical over others. Daggerfall had six endings. All of them are canon.