I guess it could be partially achieved if the following request is implemented:
[Ability to limit the scope of a relation](Ability to limit the scope of a relation)
That way the choices are objects as well. Moreover I think that this option of limiting the number of values (any number, including 1) would be better aligned with the scope of the request above.
Anyway I like your idea of having a simpler option as well: just defining a list of values. I think this is a very much needed feature.