Whether or not you have node identity should depend on the details of a given processing stage, and I think it's bad architecture to have coupling of node identity across processing stages.  I think of node identity it a bit like a C pointer in that regard, or a CPU address register, if you prefer.  I'm surprised such a matter would be relevant to an expression language as opposed to a processing spec.  But then again maybe by "Ftan" you mean some specific processing mechanism associated with Ftan.