Jacket wrote:It also kills the Tau are an Eldar experiment theory.
No it doesn't really. They said "still too young". We don't know what their plans are or used to be. Maybe they just discarded an alliance with Tau because most still don't know *BAD WORD DELETED!* about chaos and the warp so they'd make a rather inexperienced ally against the forces of chaos. Remember that it's not that long ago that Tau just experienced to what scale warfare escalates when the Imperium is serious and they were totally blown away by that experience.
Tau are still very naive and still have a lot to learn. Sure they have the technology and can adapt quick but that would be a gamble....a bigger one than allying with the Imperium in the eyes of the Eldar it seems.