Converts packages.config into PackageReference at *.csproj project file. Requires XSLT stylesheet available as second file in the gist.

Convert-ToPackageReference.ps1

Function Convert-ToPackageReference
{
    Param ( [Parameter( Mandatory, ValueFromPipeline )][String] $inputUri,
            [String] $stylesheetUri = "https://gist.githubusercontent.com/a4099181/074a6c3dd524ea0d343382137492399c/raw/cdd0fb31efd70c4c0f8c86ddb314de86ab8972e8/Convert-ToPackageReference.xsl",
            [String] $resultsFile   = [System.IO.Path]::GetTempFileName() )

    Process {
        $xslt = New-Object System.Xml.Xsl.XslCompiledTransform
        $xslt.Load( $stylesheetUri )
        $xslt.Transform( $inputUri, $resultsFile )
        Get-Content $resultsFile
    }
}

Function Update-ProjectFile
{
    Param ( [Parameter( Mandatory )][String] $projectFile,
            [Parameter( Mandatory, ValueFromPipeline )][String] $content )

    Begin   { $packageReference = '' }
    Process { $packageReference += $content }
    End     {
        $projXml = New-Object System.Xml.XmlDocument
        $projXml.Load( $projectFile )

        $nameSpc = New-Object System.Xml.XmlNamespaceManager $projXml.NameTable
        $nameSpc.AddNamespace("x", "http://schemas.microsoft.com/developer/msbuild/2003");

        $prefXml = New-Object System.Xml.XmlDocument
        $prefXml.LoadXml( $packageReference )

        $prefXml.SelectNodes( "/x:Project/x:ItemGroup/x:PackageReference", $nameSpc ) |
            % {
                $pkgNode = $projXml.ImportNode( $_, $true )
                $pkgName = $_.Include.Split('-')[0]
                $version = $_.Version

                $nodes   = $projXml.SelectNodes( "/x:Project/x:ItemGroup/x:Reference", $nameSpc ) |
                                ? Include -Like  "$pkgName*"

                if ( $nodes.Count -eq 0 )
                {
                    Write-Information "$projectFile $pkgName package outside the project file."
                    $itemGroup = $projXml.CreateElement( "ItemGroup", $nameSpc.LookupNamespace( "x" ) )
                    $itemGroup.AppendChild( $pkgNode )
                    $projXml.DocumentElement.AppendChild( $itemGroup )
                }
                else {
                    $nodes | % {
                        if ( $_.Include -Match "$version" )
                        {
                            Write-Information "$projectFile $pkgName valid reference."
                            $_.ParentNode.AppendChild( $pkgNode )
                            $_.ParentNode.RemoveChild( $_ )
                        }
                        else
                        {
                            Write-Warning "$projectFile $pkgName version mismatched."
                            $_.ParentNode.InsertBefore( $pkgNode, $_ )
                        }
                    }
                }
            }

        $projXml.SelectNodes( "/x:Project/x:ItemGroup/x:*[@Include='packages.config']", $nameSpc ) |
            % { $_.ParentNode.RemoveChild( $_ ) }

        $projXml.Save( $projectFile )
    }
}

Get-ChildItem . -Recurse -File -Filter packages.config |
    select @{ Name="ProjectFile";    Expression={ "$($_.Directory)\$($_.Directory.BaseName).csproj" } },
           @{ Name="PackagesConfig"; Expression={ $_.FullName } } |
    ? { Test-Path $_.ProjectFile } |
    % {
        $_.PackagesConfig | Convert-ToPackageReference | Update-ProjectFile $_.ProjectFile -InformationAction Continue
        Remove-Item $_.PackagesConfig
    }

Convert-ToPackageReference.xsl

<?xml version="1.0" encoding="utf-8" ?>
<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <xsl:output omit-xml-declaration="yes" method="xml" indent="no"/>

  <xsl:template match="/">
    <xsl:element name="Project">
        <xsl:element name="ItemGroup">
            <xsl:apply-templates/>
        </xsl:element>
    </xsl:element>
  </xsl:template>

  <xsl:template match="package">
    <xsl:element name="PackageReference">
        <xsl:attribute name="Include">
            <xsl:value-of select="@id" />
        </xsl:attribute>
        <xsl:attribute name="Version">
            <xsl:value-of select="@version" />        
      </xsl:attribute>
    </xsl:element>
  </xsl:template>

</xsl:stylesheet>

@aienabled Fine, well done. I'm very glad that you've got it worked out and my script is useful anyway. Yes, "usage tip" does not include downloading xslt file. It is not required while

$xslt.Load( $stylesheetUri )

is able to handle xslt file from web.

The script saved my night! Thanks!