Late to the discussion..but I agree, dead American or English elm is strong...fibrous, not brittle, hinges well.
That's a spindly tree, but not huge. I have done a few trees that required a highline...... on two, I had bombproof anchor points, so I used spectra, and set the line with minimal slack. I even had a rigging line attached to the same highline..as, like this tree, the forces were small. I've done both floating and fixed tie in points... but, the highline can be rigged through blocks and tied off at the ground, then the working points could be easily moved, if needed.
Yup, any anchor point you choose on that building can handle the relatively light loads!