Would a really short melt-zone be beneficial
There is a trade-off between the length of the melt zone and the speed at which you can print. The filament itself is somewhat of an insulator, so as the outside of the filament is heated up by being in contact with the melt zone, the inside stays cold. Therefore, the filament needs a certain amount of time inside the melt zone for the inside to fully melt. If you have a shorter melt zone, you need to print more slowly to give the filament enough time to melt. This is precisely the reason why the E3D volcano exists. It has a longer melt zone, so you can print more quickly.

You can partially compensate for a shorter melt zone by heating the nozzle up more, but there is an upper limit to how hot you can go (you don't want the outside of the filament to burn before the inside is melted).