I'm 90% sure possums are responsible for digging up my sugercane mulch. They haven't damaged my plants yet, but i'm pretty sure they will at some stage.
That setup looks brilliant!
The only issue i see with your plan is that if the wind picks up and the branch sways, it may snap your string or snap your anchors.
I cant tell from your photograph if you have one already, but i would include a trampoline spring (or similar) in there. add it where your raising/lowering rope connects to the bridle you have at the top. This way, if the wind picks up and the branch sways, the spring increases in length rather than putting too much strain on the anchors/anchor ropes.
The alternative to this may be to have the ropes loose, so that if the branch pulls on the rope, it doesn't pull on the vine.
I like the spring idea, and I really like over complicating things.