This alternate model might be a natural for use with tubes as output devices, if the complexities of the function can be overcome, as tubes are not voltage shy. For example, if a tube OTL amplifier saw an increase impedance, it would have the easier task of giving up current for voltage. On the other hand, if the impedance declines, the tube OTL is in trouble, as it must give up voltage for current. But as most, but certainly not all, loudspeakers have an impedance that spikes up from a nominal base line, this last scenario might not be a problem the amplifier would have to face.
The second model is the voltage-to-current amplifier. Here an input voltage is translated into current. For example, a one volt input might equal 4 amperes of output current. What would be the output voltage? It depends entirely on the load. If the load were a dead short, the output voltage would be zero, although the full 4 amperes would be delivered into ground.