Modify a single plane mesh to match image based on alphas, create shape keys My goal is to create the shapes of continents as they drifted from Gondwana to the present day.

My proposed approach follows, but I would welcome alternate approaches or comments on this approach.

I would like to start with a plane, subdivided. I would like to be able to modify the outside shape of the plane to match an alpha: The plane would shape to fit the alpha without eliminating any verts. I'd then create a shape key for the plane in its new shape.

I'd then like to create a new shape for that plane, based on a new alpha. I'd create a new shape key for this new shape.

The goal is to be able to create a series of shape keys on a single mesh, and be able to move between the shapes... like a tweening process between shapes.

EDIT:
The requirement is for continents which both move and change shape.



I have experimented with shape keys quite a bit, but as noted in the comments and answers suggested thus far, it's pretty nightmarish.  

I have also tried to use shrinkwrap modifiers to create shapekeys, but the shrinkwrap encloses the shape without fully conforming to it:



I don't actually need Texas as a shape, but it shows the problem with (my understanding and use of) the shrinkwrap modifier.

I have these planes on a sphere. All origins are at 0 0 0 and moving and rotating across the globe is easy... but finding a way to accurately change shapes is hard.  I understand and have used textures with alphas and displacements, but the requirement is for a level of positional accuracy and fidelity to particular dates that is ill suited to textures...  I need more constant shape modification to the continents...
If the animation will be planar (2D) I suggest you to subdivide the continents in a 2D software (Gimp, Krita, Photoshop), make a transparent PNG for each and import every continent as "Image as planes" (it's an addon), without caring the shape of the mesh; then you can set one location "jointed" and - some frames away - the location "drifted".

If it will be 3D, all PNG planes should be subdivided, shrinkwrapped to a sphere and moved with a rotation with pivot point centered in the center of the sphere.