Well, before the show starts, I'm going out on a limb here and restating my guess from above: the bones in the duffel belong to the real Raymond Reddington, and the guy that Spader has been portraying for five seasons is an imposter who does not want this fact to revealed as it would likely destroy him and everything he's done.
I mean, that would be a really big reveal.
I mean, that would be a really big reveal.