They will never be there. The problem is the passive network which has to be on the output of a digital amp in order to filter the clocking frequencies out. It is impossible to make this complex enough to filter out the clock entirely (or even enough), and not effect damping factor adversely. The sampling frequencies cannot be raised high enough with any forseeable solid state devices without incurring other losses in efficiency.

It is a lot of hoops to jump through for something which is not even as good as what we have now (the bandwidths will never match analog amps for instance). Without doubt they are the future, but thankfully I am not going to have to be part of it.