Does Mahayana Buddhism discourage attaining enlightenment under the Gautama Buddha Sasana?

As far as I've heard, Mahayana Buddhists aspire to become Buddhas themselves in the future or want to become followers of a future Buddha like Buddha Maitreya. So, are Mahayana Buddhists discouraged from attaining enlightenment within the Gautama Buddha Sasana ? If yes, wouldn't that be limiting the scope of enlightenment compared to Theravada Buddhism? Wouldn't that also make the taking refuge in the Triple gem meaningless, as they do not want to follow the teachings of the Gautama Buddha to attain enlightenment.? If the answer to the first question is 'no', any links to Mahayana specific texts which encourage one to attain Nibbana within this Sasana would be appreciated.