It’s a bit questionable if the relationship is one way, but it could be designed to be a symmetric “best” for the companion too. Okay, more CPU cycles, but this reeks of hard take-off, which probably means new physics...
Also, a bit more technically but I hope worth adding—if the companion already exists in any possible world, the fact that you engineer a situation where you are able to perceive one another isn’t creating a pattern ex nihilo, it’s discovering one. Takes some of the wind out of the argument, although you still certainly have a point on privacy if the relationship is asymmetric.
Isn’t that “hint” just an observer selection effect?
Is it surprising that the correlation between “universes that are absolutely/highly causal” and “universes in which things as complex as conscious observers can be assembled by evolution and come to contemplate the causal nature of their universe” is very high? (The fitness value of intelligence must be at least somewhat proportional to how predictable reality is...)
I worry about this “what sort of thingies can be real” expression. It might be more useful to ask “what sort of thingies can we observe”. The word “real”, except as an indexical, seems vacuous.