Dynamic Shapekeys is a Blender add-on from Vovrzull built for creating shape key animations directly in edit and sculpt mode. It works in either relative or sequential mode.
The add-on can create keyframes on the current frame or in a mode that arranges frames in dozens, and it lets you set bounding groups of vertices on shape keys. You can change the maximum and minimum values of the keys, and the keyframes it creates take those values into account. The same behaviour applies when adding a mesh.
Distributed as an add-on under the GPL license, Dynamic Shapekeys is Blender extension compatible and ships with documentation. It lists English and Japanese among its languages. A demo video is available, and update 1.1.2 improved the deletion of keyframes with restoration of key values so you can keep working.