Excellent. I favor something like "X will be implied by our best explanation of experience" rather than "X is within the visible universe", but I think broadly speaking, we're in agreement here. But note that this definition of "existence" allows me to dismiss most of Tegmark's Level IV objects as nonexistent. (Your version would allow the dismissal of more.) And of course I'm also free not to share the preference pattern of caring less about events/life-stories in proportion to their complexity.