Actually, it's not that exciting, no more so than the discovery of another minor planet (aka asteroid) or comet, and these things are being discovered almost on a daily basis. It is almost certain that there are other similarly large trans-Uranian/Kuiper-belt objects. What makes it seem important is the "10th Planet" hype (what happened to Sedna? ). If it had been reported for what it is, i.e. another Kuiper Belt Object, we'd not be nearly as exercised by it; i.e. what is exercising us is the name, not the object itself.

Some intelligent threads on this discovery on uk.sci.astronomy

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Stephen