Create-SSRS_Subscription.ps1

[string]$server = 'localhost'
[string]$serverurl = "http://$server/ReportServer_SQL2014"

$proxy = $null

# namespace parameter only works for 2010 and not for 2005 but if you get the type after setting up proxy then both works

$proxy += New-WebServiceProxy -Uri "$serverurl/ReportService2010.asmx" -UseDefaultCredential ;  #-Namespace SSRS.ReportingService2010 

# get namespace from the proxy type
$type = $proxy.GetType().Namespace

#Define Object Types for Subscription property call
$ExtensionSettingsDataType = ($type + '.ExtensionSettings')
$ActiveStateDataType = ($type + '.ActiveState')
$ParmValueDataType = ($type + '.ParameterValue')

$extSettings = New-Object ($ExtensionSettingsDataType)

# declaring an array
$extensionParams = @()
$rptParams = @()

# read the xml file with all the paramater for creating SSRS Subscription
[xml]$xml = Get-Content "C:\temp\ssrs_subscription_input.xml"
$xSubscription = $xml.Subscription
$xExtensionSettings = $xSubscription.ExtensionSettings

# ----- set variable with value available in the xml -----
$report = [string]::Join("", $xSubscription.ReportPath, $xSubscription.ReportName) 
$desc = $xSubscription.Description
$event = $xSubscription.EventType
$scheduleXml = $xSubscription.ScheduleXML.'#cdata-section'
$extSettings.Extension = $extensionSettings.DeliveryExtension

# read the extension setting parameter values
$xExtParams = $xExtensionSettings.ParameterValues.ParameterValue

foreach ($p in $xExtParams) {
	$param = New-Object ($ParmValueDataType)
	$param.Name = $p.Name
	$param.Value = $p.Value
	$extensionParams += $param
}

$extSettings.ParameterValues = $extensionParams

# ----- set variable with value available in the xml -----
$paramValues = @()
#$paramValue = New-Object ($ParmValueDataType)
#$paramValues += $paramValue
#$paramValues += $paramValue

<#
$param = New-Object ($ParmValueDataType)
$param.Name = "PASSWORD"
$param.Value = "asdfdsaf" #"S@1ram2014"
$ExtensionSettings.Value.ParameterValues += $param
#>

#$report, $extSettings, $desc, $event, $scheduleXml, $paramValues
$subid = $proxy.CreateSubscription($report, $extSettings, $desc, $event, $scheduleXml, $paramValues)

Write-Host "Susbcription was create with id: '$($subid)'"

#$subscriptions += $rs2010.ListSubscriptions($site); # use "/" for default native mode site  
#Write-Host "----- $server's Subscriptions: "  
	#$subscriptions | select Path, report, Description, Owner, SubscriptionID, lastexecuted, Status 

ssrs_subscription_input.xml

<Subscription>
	<ReportName>SSRS_Report_Name</ReportName>
	<ReportPath>/ReportFolderName/</ReportPath>
	<Description>SSRS Subscription Description</Description>
	<EventType>TimedSubscription</EventType>
	<ExtensionSettings>
		<DeliveryExtension>Report Server FileShare</DeliveryExtension>
<ParameterValues>
	<ParameterValue>
		<Name>PATH</Name>
		<Value>\\Server\SharedFolder</Value>
	</ParameterValue>
	<ParameterValue>
		<Name>FILENAME</Name>
		<Value>Report_File_Name</Value>
	</ParameterValue>
	<ParameterValue>
		<Name>FILEEXTN</Name>
		<Value>True</Value>
	</ParameterValue>
	<ParameterValue>
		<Name>USERNAME</Name>
		<Value>Domain\Username</Value>
	</ParameterValue>
	<ParameterValue>
		<Name>RENDER_FORMAT</Name>
		<Value>EXCELOPENXML</Value>
	</ParameterValue>
	<ParameterValue>
		<Name>WRITEMODE</Name>
		<Value>AutoIncrement</Value>
	</ParameterValue>
	<ParameterValue>
		<Name>PASSWORD</Name>
		<Value>Somethinghere</Value>
	</ParameterValue>
</ParameterValues>
	</ExtensionSettings>
	<ScheduleXML>
		<![CDATA[
			<ScheduleDefinition>
				<StartDateTime>2016-01-01T01:55:00.000+01:00</StartDateTime>
				<WeeklyRecurrence>
					<WeeksInterval>1</WeeksInterval>
					<DaysOfWeek>
						<Monday>true</Monday>
						<Tuesday>true</Tuesday>
						<Wednesday>false</Wednesday>
						<Thursday>true</Thursday>
						<Friday>false</Friday>
					</DaysOfWeek>
				</WeeklyRecurrence>
			</ScheduleDefinition>
		]]>
	</ScheduleXML>
	<ReportParameter>
	  <ParameterValue>
		  <Name></Name>
		  <Value></Value>
	  </ParameterValue>
	</ReportParameter>
</Subscription>

Is it working for anyone ?