This has always been a big dilemma -- to tether or not to tether. The most important thing on a long-distance race is to not become separated from the boat, because usually there is nobody around to help. In bad conditions if you fall off and are separated from the boat, is the remaining person going to be able to come back alone to get you? If the boat capsizes as a result of your falling off, will the other person be able to right the boat alone? What if you both fall off and become separated from the boat? I would rather be keelhauled a few times with the boat cartwheeling, and break a few bones, than be alone in the ocean watching my boat drift off over the horizon. And if you become separated from the boat at night, forget it.
Big-boat sailors have a relatively short tether line on their safety harness, and they can snap their tether onto attachment points on the boat or onto a "jackline" that runs fore and aft so they have mobility but cannot fall off the boat. I haven't heard any rule saying they are not allowed to use tethers because they are "attached" to the boat. I have not heard a rule saying they have to be able to have a quick-release from their tether in case the boat rolls over.
This particular rule is about hiking and trapeze harnesses specifically. They did not say you cannot be attached to the boat -- just that you have to be able to detach your trapeze harness from the boat. So are they saying that you can continue to be attached to the boat as long as it does not involve your trapeze harness? So are we now going to have to wear, in addition to life jacket and trapeze harness, a safety harness (like on the big boats) to which to fasten our tether, so we can "technically" comply to the rule?
I asked the Multihull Council if they discussed this new rule at their meeting in October, but I haven't gotten an answer yet.
Right now I do not think this rule was very well thought out, at least as to how it affects multihulls.