Yeah, the splines are pretty heavily notched already; nothing new there. Brian, I looked at the documentation, and it appears there are two designs, one threaded (12mm axle) , the other a pressure fit (15mm axle). They say you can just remove the freehub body with a sharp tug. I'm still mystified why you would do it this way, but whatever.

Re the powertap problem: I did replace the batteries, to no effect. The hub just seems to stop transmitting randomly during a ride (or rather, transmits zero power, since the computer reads 0, not dashes). I can very often get it to start up again by hopping the wheel. So, I am pretty sure it is a problem with the hub internals.