HMM. Might not be a bad idea then. I was just thinking it was another attatchment that could pop.
Quick release snaps and/or the bungee is going to be the weak link (they make one where the entire length of the tie has a little bit of give to it) But here's the thing: if you've got a puller, he'll break quick releases... but if you've got a puller, there is no safe way to tie in or to a horse trailer. He's either gonna get hurt, or break something. The pulling has to be prevented through tie training, or a tie setup that will work or is designed to break in a controlled way before the trailer is damaged, or by leaving him loose.
The benefit of the quick release at the tie point is that you can reach in and release it from the outside if they have gone down or have panicked and you can't always get to their head.