You can't simply average the km's. Suppose you estimate .5 probability that k2 should be twice k1 and .5 probability that k1 should be twice k2. Then if you normalize k1 to 1, k2 will average to 1.25, while similarly if you normalize k2 to 1, k1 will average to 1.25.

In general, to each choice of km's will correspond a utility function and the utility function we should use will be a linear combination of those utility functions and we will have renormalization parameters k'm and, if we accept the argument given in your post, those k'm ought to be just as dependant on your preferences, so you're probably also uncertain about the values that those parameters should take and so you obtain k''m's and so on ad infinitum. So you obtain an infinite tower of uncertain parameters and it isn't obvious how to obtain a utility function out of this mess.