I implemented a MonitorProjectPackageAction-class to monitor the Packages\Out-folder of the selected project. The moment a package is generated, an event will be raised. The class will wait until the file is fully written and then read the content of the sdlproj file in the sdlppx-file (which is a zip).
I am sure that the code below can be optimized, but it works :-)

CODE:
====
using System;
using System.Linq;
using Sdl.Desktop.IntegrationApi;
using Sdl.Desktop.IntegrationApi.Extensions;
using Sdl.TranslationStudioAutomation.IntegrationApi;
using System.IO;
using System.IO.Compression;
using System.Threading;
using System.Text.RegularExpressions;

namespace Dqf
{
[Action("MonitorProjectPackageAction", typeof(FilesController), Icon = "taus_icon")]
public class MonitorProjectPackageAction : AbstractAction
{
static FileSystemWatcher _watcherOutFolder;

public override void Initialize()
{
_watcherOutFolder = new FileSystemWatcher();
_watcherOutFolder.Created += _watcherOutFolder_Created;

var projectController = SdlTradosStudio.Application.GetController<ProjectsController>();

projectController.SelectedProjectsChanged += (s, e) =>
{
_watcherOutFolder.EnableRaisingEvents = false;
var pc = SdlTradosStudio.Application.GetController<ProjectsController>();
if (pc.SelectedProjects.Count() != 1)
{
return;
}

_watcherOutFolder.Path = Path.GetDirectoryName(pc.SelectedProjects.First().FilePath);
_watcherOutFolder.NotifyFilter = NotifyFilters.FileName;
_watcherOutFolder.IncludeSubdirectories = true;
_watcherOutFolder.Filter = "*.sdlppx";
_watcherOutFolder.EnableRaisingEvents = true;
};
}

private void _watcherOutFolder_Created(object sender, FileSystemEventArgs e)
{
//A new sdlppx was created. Detect if it was in Packages\out
if (!Path.GetDirectoryName(e.FullPath).ToLower().EndsWith(@"packages\out"))
{
return;
}

//It was in Packages\Out!
FileInfo fInfo = new FileInfo(e.FullPath);
while (IsFileLocked(fInfo))
{
Thread.Sleep(500);
}
using (ZipArchive zip = ZipFile.Open(e.FullPath, ZipArchiveMode.Read))
foreach (ZipArchiveEntry entry in zip.Entries)
if (entry.Name.EndsWith(".sdlproj"))
{
string packageGUID = ReadPackageGUID(entry);
if (packageGUID!=null)
{
//TODO@@@ Create child project, etc.

return;
}
}
}

private static string ReadPackageGUID(ZipArchiveEntry entry)
{
string packageGUID = null;
string tempFile = Path.GetTempFileName();
File.Delete(tempFile);
entry.ExtractToFile(tempFile);

using (StreamReader sr = new StreamReader(tempFile))
{
sr.ReadLine(); //Skip first line with xml definition
string pp = sr.ReadLine();

Match m = Regex.Match(pp, @"PackageGuid=""(.+?)""");
if (m.Groups.Count == 2)
{
//Done!
packageGUID = m.Groups[1].Value;
}
else
{
//Unexpected error. The sdlppx file has not a PackageGuid
}
}
File.Delete(tempFile);
return packageGUID;
}

static bool IsFileLocked(FileInfo file)
{
FileStream stream = null;
try
{
stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
}
catch (IOException)
{
return true;
}
finally
{
if (stream != null)
stream.Close();
}
return false;
}


/// <summary>
/// The user has selected multiple files and wants to add DQF settings for those files
/// </summary>
protected override void Execute()
{
}
}
}

I implemented a MonitorProjectPackageAction-class to monitor the Packages\Out-folder of the selected project. The moment a package is generated, an event will be raised. The class will wait until the file is fully written and then read the content of the sdlproj file in the sdlppx-file (which is a zip).
I am sure that the code below can be optimized, but it works :-)

CODE:
====
using System;
using System.Linq;
using Sdl.Desktop.IntegrationApi;
using Sdl.Desktop.IntegrationApi.Extensions;
using Sdl.TranslationStudioAutomation.IntegrationApi;
using System.IO;
using System.IO.Compression;
using System.Threading;
using System.Text.RegularExpressions;

namespace Dqf
{
[Action("MonitorProjectPackageAction", typeof(FilesController), Icon = "taus_icon")]
public class MonitorProjectPackageAction : AbstractAction
{
static FileSystemWatcher _watcherOutFolder;

public override void Initialize()
{
_watcherOutFolder = new FileSystemWatcher();
_watcherOutFolder.Created += _watcherOutFolder_Created;

var projectController = SdlTradosStudio.Application.GetController<ProjectsController>();

projectController.SelectedProjectsChanged += (s, e) =>
{
_watcherOutFolder.EnableRaisingEvents = false;
var pc = SdlTradosStudio.Application.GetController<ProjectsController>();
if (pc.SelectedProjects.Count() != 1)
{
return;
}

_watcherOutFolder.Path = Path.GetDirectoryName(pc.SelectedProjects.First().FilePath);
_watcherOutFolder.NotifyFilter = NotifyFilters.FileName;
_watcherOutFolder.IncludeSubdirectories = true;
_watcherOutFolder.Filter = "*.sdlppx";
_watcherOutFolder.EnableRaisingEvents = true;
};
}

private void _watcherOutFolder_Created(object sender, FileSystemEventArgs e)
{
//A new sdlppx was created. Detect if it was in Packages\out
if (!Path.GetDirectoryName(e.FullPath).ToLower().EndsWith(@"packages\out"))
{
return;
}

//It was in Packages\Out!
FileInfo fInfo = new FileInfo(e.FullPath);
while (IsFileLocked(fInfo))
{
Thread.Sleep(500);
}
using (ZipArchive zip = ZipFile.Open(e.FullPath, ZipArchiveMode.Read))
foreach (ZipArchiveEntry entry in zip.Entries)
if (entry.Name.EndsWith(".sdlproj"))
{
string packageGUID = ReadPackageGUID(entry);
if (packageGUID!=null)
{
//TODO@@@ Create child project, etc.

return;
}
}
}

private static string ReadPackageGUID(ZipArchiveEntry entry)
{
string packageGUID = null;
string tempFile = Path.GetTempFileName();
File.Delete(tempFile);
entry.ExtractToFile(tempFile);

using (StreamReader sr = new StreamReader(tempFile))
{
sr.ReadLine(); //Skip first line with xml definition
string pp = sr.ReadLine();

Match m = Regex.Match(pp, @"PackageGuid=""(.+?)""");
if (m.Groups.Count == 2)
{
//Done!
packageGUID = m.Groups[1].Value;
}
else
{
//Unexpected error. The sdlppx file has not a PackageGuid
}
}
File.Delete(tempFile);
return packageGUID;
}

static bool IsFileLocked(FileInfo file)
{
FileStream stream = null;
try
{
stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
}
catch (IOException)
{
return true;
}
finally
{
if (stream != null)
stream.Close();
}
return false;
}


/// <summary>
/// The user has selected multiple files and wants to add DQF settings for those files
/// </summary>
protected override void Execute()
{
}
}
}