Yes, but in worlds where not every sequence {0,1} * is equally likely (eg, your possible worlds have ANY structure) there will be predictors that outperform random predictors (like AIXI for example).
(this is not literally true up to maximum pedantry (eg. there are infinitely measures on all languages where AIXI/​solomonoff induction never works, but for all of those see my other comment))
Yes, but in worlds where not every sequence {0,1} * is equally likely (eg, your possible worlds have ANY structure) there will be predictors that outperform random predictors (like AIXI for example). (this is not literally true up to maximum pedantry (eg. there are infinitely measures on all languages where AIXI/​solomonoff induction never works, but for all of those see my other comment))