RE: the event itself -> I now see the distinction, thanks for the clarification.  I was thinking that this could be inferred from the general event, but if a usage_id was shared (is that possible?) it would be difficult to tease apart the split test vs. other viewing events.

RE: the naming convention.  I see now that you are thinking about this module as not being part of the core platform, which is fine.  I agree that forcing a clean structured hierarchy is probably difficult or even impossible, however, we've found it pushes people to think through what the event is and how its related to others so I think its worth it even if the hierarchy ends up being a bit chaotic.  xblock.split_test.child_rendered seems reasonable.  You should update @sarina's event though too since it currently uses "edx."