arch, pretty cool and inventive approach!
However, I would be concerned that tie downs so low have poor leverage against the bike "wanting" to move around as opposed to tie downs attached to the bike at a higher point, and this may cause a potential issue if you hit a really bad bump or a pothole on the road. To compensate for such deficiency, you have to tighten tie downs harder to achieve a few times more force than you would ordinarily achieve with regular approach. So, use properly rated tie downs. Notice that in case of using Pit Bull stand in similar way, the role of tie downs is performed by metal tubes - a lot stronger and non-stretchable material.
I wouldn't be concerned about the suspension when utilizing traditional method to tie the bike down - just don't over tighten the tie downs. Half way through suspension travel is OK. Bad things happen when people ratchet it up and completely compress the suspension. I have many thousands of miles on the trailer, and never a problem with suspension.
Neat approach nevertheless! Probably quicker than with regular tie downs, too.
Also, consider extra tie downs to cover 'single point of failure' scenario. You don't want to be wondering doing highway speed, possibly in the dark - what's going on with your bike. Also, the white tubes on either side of the rods - if they are plastic, try to replace with metal.
Also, I would use another washer along with a locking washer between the hook and the nut: hook, then washer, then locking washer, and then nut.
Is the tie down goes straight down (ideal scenario), or away from the hook?
Really cool idea! I should think about it.