Lurking on cheezeburger I find a post discussing how King Sombra and Princess Platinum could might have been related on the basis that:
-They reigned ~1000 years ago
-King Sombra and Princess Platinum are both unicorns
-Both likes shiny things (crystals)
-Her people left behind a cold barren wasteland in search of greener pastures... or just green in general at the time.
-Her cloak has some semblance to King Sombra's
Now, while this all sounds fine and dandy there's also:
-Princess Wet Platinum leads the unicorns, not crystal ponies. In fact crystal ponies don't even have horns or wings. Either Sombra marauded a second kingdom or something freaky happened over the last 1000 years
-1000 years seems like a staple in the Equestrian timeline. It's like Princess Celestia got high and wrote history books replacing every missing date with "a thousand years ago". When did I banish Nightmare Moon to the moon? A thousand years ago. When did Discord turn into a stone? Uh... I'm going to say a thousand years ago. Hm... did Twilight move to Ponyville two months ago or three months? Oh well, I'll just say she arrived a thousand years ago.
-King Sombra can terraform harder than 1000 Minecraft guys at once and Princess Platinum can't. I actually meant 40 Minecraft guys, but a thousand sounds cooler.