It would be angled while on a table, uncomfortable to hold, and the teardrop shape limits potential space for components as opposed to a flat back
If u look at the teardrop case design, it is so subtle. I believe u wouldn't really even feel a difference let alone feel awkward in your hands. Obviously the design came from somewhere. And I'm sure apple has considered the fact that the phone is held in landscape for basically everything but talking on the phone. So I think if it has any taper at all it will be perfectly natural.
And the biggest component is the camera. Which is why the top would be "fatter" then the bottom. A slight taper would give the illusion that the device is thinner then it actually is. The same concept was used on iPad 2 with the beveled edge. It was done to make the iPad look thinner.