You can't define a _sort expression with types other than Link

(Incomplete Feature, To be Fixed , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Functions
Summary: That is, you can't say _sort(EXP) if the received Type isn't Link. _sort just doesn't cope with that yet.
A real-world example where I want this comes from the Poker Space. In that user value expression, I want to be able to say:
_sort(_userValueThing -> Display Name)
and sort the results as expected. But in fact, since User Value is its own meta-type, and doesn't implement doComp (yet), it just chokes. All of the fancy sort-on-expression logic doesn't work unless you're talking about a Link to a Thing.
The implication is that _sort needs to be generalized. All that code that is Link/Thing specific should get generalized, including the notion of the fallback.