I have seen a couple of instances of を being used at the end of sentence. From my limited knowledge, を is supposed to be used to indicate the direct object of a verb, but I have seen it following a verb, or just completely at the end of a sentence.
It's a rhetorical style often used as an exhortative. We also see phrases ended with particles in other contexts and we can loosely compare it with when we use a prepositional phrase alone in English (although we don't have a particle for marking an object of a verb in English). Sentences such as 未来を！ 夢を！are difficult to translate. They imply action without specifying the action or the actor and invite a listener or reader to supply their own.