Ultimately, we used a wire brush attachment that we put on a air grinder to slowly remove the compound. The softer drywall compound came off the wall fairly easy but in the last corner we ran across a slightly yellow filler that was a lot harder than drywall compound.
Blog reader, Alex, suggested spraying the drywall compound with water. This worked great after we removed the majority of the compound and was left small amounts in the textured areas of the plaster. After spraying the residue with water, I used a wire brush to get the remaining tidbits.
Tomorrow we will get back to the kitchen ceiling and I can't wait because I need a break from scraping.
FYI the white area in the shape of Florida without a pan handle is an area where the plaster is missing and it filled with drywall compound. We are leaving this area for the plaster guy to decide what to do. It's currently recessed about 1/2 inch below the surface of the wall. I don't know if he will fill that area or if he will need to remove what is there and fill with patching plaster.