Current state is that if you want to retrieve value of a given variable (variable of a parametric cell) via expression in item property definition you can do it but in limited way.
(item type is attached to the parametric cell afterwards in model not prior when defining the cell)
First problem is that in the expression code a variable is not called by a name but by a index from a global array (which probably does not always strictly correspond to the order of variables of parametric cell).
Second problem is that you can only get value as string without info about corresponding units.
For better functionality it should be much easier to do this with shorted code something like: get.this.parametric.cell.variable"nameofvariable"
The discussion for this is elaborated in this post: