The selection of the proper reference class is a serious problem for anthropic reasoning. But perhaps anthropic reasoning is not necessary to take advantage of a theory of everything.
Consider how an non-sentient being (excluded by most proposals for the reference class) can use a TOE. Imagine a non-sentient oracle that was built to accomplish some goal (for example to maximize some definition of social welfare) by answering questions people send it. The oracle could work by first locating all instances of itself with significant measure which are about the answer the question it's considering (by simulating all possible worlds and looking for itself in the simulations). Then for every potential answer, it computes the approximate consequences for the meta-universe if all of its instances were to give that answer. Finally it gives the answer that would maximize the value function. Sentient beings can follow the same decision procedure used by the oracle. Suppose you are faced with a bet involving a tossed coin. There is no need to consider probabilistic questions like "what is the probability that the coin landed heads?" which would involve anthropic reasoning. You know that there are worlds where it landed heads and worlds where it landed tails, and that there are instances of you in all of these worlds which are indistinguishable from each other from the first-person perspective. You can make the decision by considering the consequences of each choice if all instances of you were to make that choice.