The problem of eschatological verification seems no greater than simply asking why God doesn't prove his existance here. And besides, you're assuming you get to gates of Heaven and instantly recognize what's happening. In reality, an afterlife prior to judgement would only show that belief systems involving an afterlife are correct, and there are still thousands of those to choose from. And any number that could be modified or started in the afterlife.
If everybody came up after their graves at the end of the world, there is no logical reason why nonbelievers would not still be nonbelievers. They would say, "well that was a surprise, but where is this Jesus you were talking about?" And eventually some kind of speculation about accidental time travel would could about that, while unusual, would seem more probable than the entire virgin birth/died for your sins thing.
My prediction, anyway.
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