> * Subtree root
> > :PROPERTIES:
> > :EXPORT_Variable: Test> > :END: 
> > {{{Variable}}}
> > Would something like this be possible?
> > Best,Joon
> 
> It is:
> 
>   {{{property(EXPORT_Variable)}}}
> 

Thank you so much! This will be very useful. 
One related question - I'm including another subtree (I'm using 8.3beta) using
   #+INCLUDE: "playground.org::*Contents" :only-contents t
but it seems I cannot access the property of the parent heading inside the included subtree. (Using {{{property(EXPORT_Variable)}}} to access the parent property). Is this not possible?
Thank you so much,Joon