Thanks for all the input fellas.
X: The cable anchors would need to be above head level. I have zero faith in the average drunken student! It would be ironic to end up with a lawsuit totally unrelated to the original tree concern!
A few questions:
1.) would the cables run horizontal or sloping upwards?
2.) Dynamic vs. static? If dynamic, the anchors would be even more limited, according to natural crotches available. Also what about shock absorbers? What about my idea of inserting extras in each span? Or should the movement be eliminated as much as possible?
I'll get back to you on the dbh.
Guy and Boreality: I'm exagerating to say this keeps me up but thanks for the concern. I'm pretty sure my CYA is in place. I have another tree with a different hazard and no support (from above, not in the tree!) so I'm well aware of my paper trail. For both trees I've already recommended "further detailed assessment required" , including Philip's involvement. Seeing as I'm getting so much help on this one maybe I'll add the other tree onto this thread!
I thought the conks are Ganoderma lucidum but I'm not really good with fungi. I'll take better photos tommorow and post them.
I guess another question is how to tell if this is getting worse over time? A tree with a butt already this ugly, conks and so little cambium, at what point IS it dangerous? How much uglier would this need to be?!? The canopy is still really healthy so who knows what this thing can still do...