I'm not as versed in this trilemma as I'd like to be, so I'm not sure whether that final question is rhetorical or not, though I suspect that it is. So mostly for my own benefit:

While there's no denying that subjective experience is 'a thing', I see no reason to make that abstraction obey rules like multiplication. The aeroplane exists at a number of levels of abstraction above the atoms it's composed of, but we still find it a useful abstraction. The 'subjective experiencer' is many, many levels higher again, which is why we find it so difficult to talk about. Twice as many atoms doesn't make twice as much aeroplane, the very concept is nonsense. Why would we think any differently about the conscious self?

My response to the 'trilemma' is as it was when I first read the post - any sensible answer isn't going to look like any of those three, it's going to require rewinding back past the 'subjective experience' concept and doing some serious reduction work. 'Is there twice as much experience?' and 'are you the same person?' just smell like such wrong questions to me. Anyone else?

Nick, will have a look at that Bostrom piece, cheers.