I hate to be terribly mundane, but the Old House Journal published a book
within the last 5 years (edited by Patricia Poore) which I constantly refer to
on items like this.  (The truth is out!).  Lately people are patching plaster
with sections of drywall, then taping and giving a feather-edged skim coat
over the patch.

If you patch with natural plaster be absolutely sure it has completely dried
out prior to priming and painting. I'd wait a few weeks.

Anne