Not understanding you. For sure if it's a List today is doesn't look good to expose it as a List.

    This way I can be sure that there are no duplicates when I check.
Well that needs a Set right?

    but in the future this behavior might change in some way
"Some way" ? Would be nice to clarify if _conceptually_ you will ever need duplicate options, or if that's terribly wrong.
Think of it as an annotation, you can't add the same annotation twice on the same field/class/method. Would the Option conceptually work like an annotation?

A List also expresses a sense of sequence. Do you see any usefulness of that?