Unlike Ghostway, which saw a recent price spike due to actually becoming the centerpiece of a viable Modern deck, there aren't any top decks currently using Order of Whiteclay. But his effect is actually quite good. With it, you can return a target creature with converted mana cost 3 or less from your graveyard to play. The trick about his ability: you have to untap him.
There's a clever interaction here with Springleaf Drum. You can use the Drum to tap any creature down for one of any colored mana. Then it's easy enough to untap Order of Whiteclay to use his ability. The question then remains, what creatures will you want to bring back, and how will you facilitate them getting there?
One list that I found online,By the Order of Whiteclay on MTG Vault, has some good ideas. It's a white/black deck that is focused around hand control. Not only does it use the traditional discard spells such as Inquisition of Kozilek and Thoughtseize, but it also uses creatures like Tidehollow Sculler and Brain Maggot to deprive your opponent some more. It also plays Kitchen Finks for lifegain and the Persist ability and Phyrexian Rager for card advantage. It also plays one Banisher Priest to deal with big creatures. To get those creatures in the graveyard are 2 Viscera Seer, which allow you to sacrifice a creature to Scry 1, and a full playset of Bloodthrone Vampire. The Vampires allow you to sacrifice a creature to gain +2/+2 until end of turn.
It's an interesting list to be sure, and I'd like to see this sort of deck in action. I'm not sure what the endgame would look like, though. Since you have the Springleaf Drums, you could run more colors. If you have the budget for it, a card like Fulminator Mage could help the deck by holding opponents back by destroying non-basic lands. Tarmogoyf would give the deck a more potent threat, as well. While the hand control idea seems cute (there are 4 Sin Collectors in that MTG Vault deck's sideboard), Tidehollow Sculler and Brain Maggot have temporary effects. If this type of deck is going to succeed, it's going to need a consistent way to win. 3 mana to reanimate isn't terrible, but it's still a bit slow for competitive Constructed environments, especially Modern.
There's another explanation for the sudden speculation: a very popular Commander by the name of Alesha, Who Smiles at Death. Her ability can bring back a creature with power 2 or less from the graveyard into play tapped and attacking. Being only a 1/4, it's likely it will survive combat. Plus, it reanimates a lot of things in the deck. While it can't use the untap ability immediately after Alesha brings him back (unless he otherwise gains haste), he's bound to be able to attack at other points and bring back a useful creature from the grave. Alesha plays a lot of CMC 3 or lower creatures with useful effects, so it's not hard to see this not included in a lot of Alesha lists. There's a great article about Alesha on Hipsters of the Coast.
The other explanation for the speculation is the rapidly growing Tiny Leaders variant of Commander, where you can only play cards with CMC 3 or less. Order of Whiteclay most definitely fits that mold, and since Alesha is a fine Commander in that format, as well, is doubly a good reason to have this card have a sudden jump in popularity.
If you can find Order of Whiteclay in a bargain bin somewhere, go ahead and pick them up. But it doesn't seem like a $5 card yet. It has a great effect, but it seems speculators have jumped the gun a bit looking for the next big Modern deck. It worked with Ghostway, but we'll see how Whiteclay holds up. Shadowmoor is a set with fairly low supply at this point, so once the market settles, it's probably not a bad card to have around regardless.