To get this to work you need to manually add two XSD files, once you have added them you will get Instellisense.
First open any random XML file, once you have opened it you will notice that the menu bar will have a new menu item called XML.
Next navigate to XML > Schemas > Add
Next enter the path in the filename box C:\Program Files (x86)\MSBuild\Xamarin\Android and hit enter
You should see two XSD files, select them both by holding shift and clicking on each.
Click on Open and you should see the files have been added in the XML Schemas dialog
Click OK in the Schema Dialog
and then close the XML file and reopen an XML or AXML and you should get intellisense as soon as you type <.
Hope this helps someone.