Are there any good sources of documentation on the file format of picasa.ini files
Here is a good one .picasa.ini decoded reverse-engineered for Picasa Version(s): 3.8.0 by Franz Buchinger
You might want keep track of the following feature request for Shotwell #1930 (Import albums/meta info from Picasa)
And have a look at avpicfacexmptagger for ideas.