Subtypes for input constant nodes

Properties of node groups have subtypes that can utilize the unit system like for example if a Vector property is set to Translation subtype it accepts length units:

Input nodes do not:

This creates problems for working with different than default unit settings. It would be nice if it was possible to define subtypes for the data in input nodes as well. It would also be nice if they could automatically get the subtype from whatever they are plugged into to avoid mismatches.