We can't use Solomonoff induction - because it is uncomputable.

Generating hypotheses is uncomputable. However, once you have a candidate hypothesis, if it explains the observations you can do a computation to verify that, and you can always measure its complexity. So you'll never know that you have the best hypothesis, but you can compare hypotheses for quality.

I'd really like to know if there's anything to be known about the nature of the suboptimal predictions you'll make if you use suboptimal hypotheses, since we're pretty much certain to be using suboptimal hypotheses.