@sspomer: What I've been trying to say is, that if you ride Enduro in SoCal, such a bike might be top of the list, but maybe not, if you're riding Enduro in the Italian Alps.
It wont be a very good allrounder, but perfect for fast and open trails. I think current 29ers are still a fair bit from " too much for anything other than pedaling up a fire road". But of course it depends on what exactly you're referring to by long and slack. The Intense above might be too much for most trails; the new Nukeproof could surely go a bit longer by going slacker.
C. Porter claims to have found the limits for trail bike geometry. However, this may be true for his riding style and type of trails. I also wonder why - except for very few frames like the new Rune - headangles for 650b bikes haven't gotten a lot slacker recently.
I personally think that 180mm would be overkill for a 29er also in terms of required chainstay length. But to judge, it would be necessary to ride it and look at the time.