How would an instant or sorcery with an effect that targets work with Feather?
Shoulder to Shoulder is an instant or sorcery spell that targets; it doesn't matter that the word target only appears in the reminder text.


  114.1e Some keyword abilities, such as equip and provoke, represent targeted activated or triggered abilities. In those cases, the phrase “target [something]” appears in the rule for that keyword ability rather than in the ability itself. (The keyword’s reminder text will often contain the word “target.”) See rule 702, “Keyword Abilities.”


So Feather's ability applies to Shoulder to Shoulder, and it's exiled as it resolves.