This task wouldn’t require much efforts but:

• Service Fabric doesn’t support packaging its “package” (which is not a real package but just a directory) into .sfpkg out-of-the-box. Only suggests to use ZipFile.CreateFromDirectory.
• MSBuildTasks doesn’t support .NET Core so we can’t use its Zip task. So we have to write our own instead.
• .NET Core doesn’t support CodeTaskFactory. Soon it will (see the same issue, in the bottom) but for now we can use RoslynCodeTaskFactory

Here’s the full project, I called it package.props and imported from all my sfproj:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="..\packages\RoslynCodeTaskFactory.2.0.7\build\RoslynCodeTaskFactory.props" />
  <UsingTask TaskName="Zip"
             TaskFactory="CodeTaskFactory"
             AssemblyFile="$(RoslynCodeTaskFactory)"
             Condition="'$(RoslynCodeTaskFactory)' != ''">
    <ParameterGroup>
      <SourceDirectoryName ParameterType="System.String" Required="true" />
      <DestinationArchiveFileName ParameterType="System.String" Required="true" />
    </ParameterGroup>
    <Task>
      <Reference Include="System.IO.Compression.FileSystem" />
      <Using Namespace="System.IO.Compression" />
      <Code Type="Fragment" Language="cs">
      <![CDATA[
        try
        {
          if (File.Exists(DestinationArchiveFileName))
          {
            Log.LogMessage("File {0} already exists, deleting.", DestinationArchiveFileName);
            File.Delete(DestinationArchiveFileName);
          }
          string directoryName = Path.GetDirectoryName(DestinationArchiveFileName);
          if (!Directory.Exists(directoryName))
          {
            Log.LogMessage("Directory {0} doesn't exist, creating..", directoryName);
            Directory.CreateDirectory(directoryName);
          }
          Log.LogMessage("Zipping directory {0} to {1}", SourceDirectoryName, DestinationArchiveFileName);
          ZipFile.CreateFromDirectory(SourceDirectoryName, DestinationArchiveFileName);
          return true;
        }
        catch(Exception ex)
        {
          Log.LogErrorFromException(ex);
          return false;
        }
      ]]>
      </Code>
    </Task>
  </UsingTask>
  <Target Name="Package" DependsOnTargets="$(PackageDependsOn)" AfterTargets="Build" Returns="@(_AllPackageFiles)" />
  <Target Name="ZipPackage" AfterTargets="Package">
    <PropertyGroup>
      <PackageSource>pkg\$(Configuration)</PackageSource>
      <PackageDestination>sfpkg\$(MSBuildProjectName).sfpkg</PackageDestination>
    </PropertyGroup>
    <Zip SourceDirectoryName="$(PackageSource)" DestinationArchiveFileName="$(PackageDestination)" />
  </Target>
</Project>

It will zip folder pkg\Release to sfpkg\.sfpkg.

Now call the Package target using PowerShell:

param
(
[Parameter(Mandatory=$true)]
[ValidateSet('Debug', 'Release')]
[string]$Configuration
)

$projects = Get-ChildItem *.sfproj -Recurse
foreach ($project in $projects)
{
  Write-Host "Packaging project $project and configuration $Configuration"
  & msbuild "$project" /t:Package /p:Platform=x64 /p:Configuration=$Configuration /m
}

That’s it. Now you can take the resulting sfpkg and deploy it directly to your Service Fabric cluster.