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...