I think I would have gone with Diamond Tiara Rich.

They can try to hide it all they want, but that Wonderbolt is buckin’ Surprise!

If they were smart they would legal-ese their way past that because I can’t remember what it was for, but if used as a name (Both cap’d) those can be copyrighted in a sense. (ala Wendy the Witch can be copyrighted as Wendy Witch)
 
Spitfire is uncommon enough one could land it in the same category as The Goon.  
Soarin’ is safe due to apostrophe.
 
Essentially if they change anyone other than the flower trio they need to fire their lawyers, as you can’t confuse asking for Apple Fritter the pony with Apple Fritter the desert.
 
Also it kind of makes sense Diamond would have a middle name since she’s all snooty, and would probably use it when pissed off (or her dad might use it on her)  
Expect similar treatment for Silver Spoon and the Canterlot ponies like Fancy Pants.

My guess is that they couldn’t trademark “Diamond Tiara” and tried to fix it by adding an extra name.  
It’s happened several times before, with Rose (Roseluck), Daisy (Flower Wishes), Caramel (Chance-A-Lot), Trixie (Trixie Lulamoon), Apple Bumpkin (Apple Dazzle) and Red Gala (Crimson Gala)
 
…which makes me really concerned about the incoming Lily, Bon Bon, Soarin’, Spitfire, Apple Fritter and Caramel Apple…

I need zat PHOTO FINISH!  
DAS IST SCHÖN!

@ace: You’d think so, but it’s actually launching with a re-release of the Pony Wedding and Cloudsdale sets, basically replacing the Apple Family set…which, come to think of it, makes sense now that we know they’re making another set with Applejack in it.

So, I guess Pinkie’s set will be launched alongside Fluttershy’s?

IKR. I was hoping Cheerilee would have rounded out the AB/DT set, but we just get another Applejack.

Lousy goddamn stupid chinese characters, I want to read the set’s names!
 
Anyway, I have no idea where they hell the pulled that ‘Dazzle’ off, but it sounds fucking awesome! Seriously, dazzle is one of my favorite words, and suddenly, it becomes the middle name of one of my favorite ponies!
 
…
 
And what the hell is AJ doing there?

I wouldn’t be surprised if there was an AJ in every generation of the toys. She’s definitely one of the earliest releases.

Applejack may be the main 6 member with the least episodes, but she sure has a lot of toys.

“Diamond Dazzle Tiara”?

Ah yes, the Wonderbolts pony known as……..Wonder Bolts.