It's now possible to edit shape keys in object mode using the Flexi Edit tool of the Bézier Toolkit. This video shows you how.
Add-on Download Location: https://github.com/Shriinivas/blender...
Script File: blenderbezierutils.py
Bezier Toolkit Video Tutorials (includes installation instruction and primitive shape tutorials): • Bezier Toolkit
Modifying Vertex Count of a Shape Key Without Distorting Curve: • Blender 2.8 Tip - Retain Curve Shape Keys ...