Why system properties are not resolved with blueprint's external property-placeholder ?

Issue

• Camel blueprint does not accept external properties. Either custom or predefined like karaf.etc. Need to pass external folder location specified as ether environment property or system property.
• Hardcoded filepath in camel blueprint works fine.
• Environment or System variables are not resolved to actual value when used with ext:location tag. Below is the blueprint snippet

 <ext:property-placeholder placeholder-prefix="$(" placeholder-suffix=")">
        <ext:location>file:${karaf.home}/etc/application-config/test/test.account.properties</ext:location>
    </ext:property-placeholder> 
    <ext:property-placeholder placeholder-prefix="[[" placeholder-suffix="]]">
        <ext:location>file:/path/to/es-datasync.account.properties</ext:location>
    </ext:property-placeholder> 

• My blueprint definition for property-placeholder files works, but it is too restrictive for our needs, in that:
• The files must live in ${fuse.home}/etc
• They must end with ".cfg"
  • We need to move these files into a sub-folder of ${fuse.home}/etc AND want to change the extension to ".properties". Something like this...

${fuse.home}/etc/application-config/test/test.account.properties
${fuse.home}/etc/application-config/test/test.fuse.env.properties