In particular, what are the implications for existential risk reduction?

We could be getting most of our measure from all sorts of places, which means that maybe a very small proportion of our measure is actually at stake. If all computations exist, some of those computations have preferences over other computations that include us. It might be good to understand such preferences. That in itself has many implications. But I guess I'd say that it's easy to go funny in the head when thinking about things like that, so be careful.