would have been 一定为虚拟语气?

would have been 还可以表示过去将来完成时
如：he told us that he would have finished his paper by that time.过去将来完成时一般都说过去某个未完成的任务将会完成 例如 XX would have finished it by 3 p.m.。该句话怎么理解呢？1896年认为以后将变得impossible？1896已经impossible了 ， 用过去将来时就可以了，完成时怎么理解呢？我仔细听了一下听力，没有听到have这个单词，文稿应该是would be impossible，be与 im连读之后会听成been，但绝没有出现have。所以正确的应该是：The London Olympics are about to begin, and spectators will again be riveted by feats that would be impossible when the modern Olympics began in 1896.