A constant airflow (in my head) would eventually make the teardrop shape, but it would take literally forever, because of the equivalent force necessary to maintain attached flow while eroding the structure.
First, the erosion would round the forward corners. After that, if the flow were maintained in the same direction, the flow would be subject to boundary layer adhesion, and the majority of erosion would occur still at the front, but some erosion would now also occur at the sides, although to a much lesser extent, since the blunt force of the flow occurs at the leading face, and the rest is subject to energy expended to maintain attached flow. The next thing to be rounded would be the rear, due to the vortex effect creating a vacuum behind the brick.
This creates an egg shape.
The next effect is still a matter of attached flow, but as you can see (from my thought) the majority of effects after the front erosion allows for attached flow is from vortices drawing on the structure of the object. The eventual erosion of the tail section (beyond the widest point of the tear drop) should actually occur from the back to the front, and should occur at a rate equivalent to the energy being expended in the vortex, which decreases as the vortex gets smaller.
In other words, if you were to divide the events into time sections, the first section would be the erosion of the face into a mostly rounded object which represented a shape that (at the constant wind speed and direction) would maintain attached flow along the surface of the object in question.
The second time period would be the rounding of the trailing edges of the object, as well as surface erosion of the length of the object on all contacted sides.
The third time period would be the eventual erosion of the object into a form that would allow for perfectly attached flow along it's entire surface, with no vortex created at the trailing edge.
The fourth time period would encompass the eventual complete erosion of the object, as it basically went from an originally sized object of optimal shape, to a smaller and smaller object of the same optimal shape, until the object was completely eroded into basic components.
(The linearity of the thought requires that the bonding structure of the object be exactly uniform at any point in it's body.)
Man, I love thinking about dumb stuff...
