I've never ice-bathed our rabbit meat (unless you count putting them in stock pots filled with hose water that comes from a glacier an ice bath
). We have always done similar to what you do. It's rinsed and then goes into the cold-water pots, then into the refrigerator still in those pots, where they are left for 3+ days. (Honestly, I leave them in the pots in water because I don't have room for that many baking sheets and I'm too lazy... um, I mean busy... and cheap to cover them with plastic wrap.) In my experience it's that all it takes to keep the meat from being chewy. On the other hand, I did put them straight from harvest into the freezer for a while, and that seemed to do just as well. But I find it's a lot easier dealing with the meat when you want to use it if you don't have to thaw it first. I'm looking forward to hearing what you find with your test processing.
I am not even too picky about how long it sits in the refrigerator (I do try to limit it to about a week). Since I can most of it these days, I get to it when I get to it (or when I need room in the fridge!). In the meantime the kids pull it out when they want meat in their burritos, and sometimes I end up with nothing to can.
My husband has been hunting and trapping for almost 50 years, and is very particular about how meat is handled. The "never soak meat in water" mantra went out the window a long time ago. When he harvests large game, he guts it and immediately drops it into a stream, which is always quite cold due to above-mentioned glaciers. Usually it's several days before they get home to process the meat and put it in the freezer. We never fail to hear guests comment, "This is the best ________ I've ever tasted."
As for the USDA, they're the folks that bring us the meat in the store, so, uh, no thanks. I recently had sad reason to visit a "USDA-licensed" butcher facility and I was aghast that any place like that still existed. It wasn't exactly like Sinclair's
The Jungle, but it probably felt like that to the animals. I am not a particularly sentimental or emotional person, but I had a hard time sleeping for the next two nights.