Now that we've got a taste of all the Mane Six parents after 7 seasons, I thought I'd take a crack at them. Since I'm a bit of a genealogist as a hobby, I thought it'd be fun to take an extra step and formulate some headcanons concerning the Mane Six's heritage. Yeah, it sounds silly at first considering we're dealing with magic talking horses in an entirely fictional setting, but much of the accents, fashions and environments in the show have a clear basis in real-world cultures, so whatever nationality I list here, I'm sure there's some equivalent in the show.
Since the major setting of My Little Pony is largely influenced by European folk art and fairy tales, I centered much of the characters' heritage around that region. If I'd made the ancestries too all-over-the-place, it would've just felt like artificially pushing diversity for its own sake.
*Night Light's German was taken from his basis in the German G1 pony "Nachtlicht", while his Russian was lifted from Tara Strong's own ancestry. For Twilight Velvet's Japanese, there was this minor "High Expectations Asian Father" meme that was associated with Mr. Sparkle at one point and I just transferred the ethnic aspect over to the Mrs.. Besides, I figured if anyone in the Mane 6 would be the token minority, it may as well be the lead :P
*A lot of the country stars Applejack's voice was modeled after (Dolly Parton, Miley Cyrus, etc.) have ancestry hailing from England, Ireland and sometimes Germany, so I had Bright Mac's ancestry mirror that with some Swiss-German to tie into Pinkie's potential distant relationship. Pear Butter's big frizzy red hair and freckles just screams Celtic blood, so I lent her a good part of that Irish too. Meanwhile, the French comes from the whole "Grand Pear / grandpere" thing and the Austrian-German comes from William Shatner's ancestry and the fact that the earliest traces of pear cultivation were found around that region (northern Germany, actually, but close enough).
*Pinkie's folks are clearly modeled after the Amish, who widely descended from German-speaking Switzerland, so I thought it safe to bet that Pinkie would be fullblood Swiss-German.
*Seeing how unabashedly Midwestern Rarity's parents are, I saw it fit that they'd both have some amount of Scandinavian blood to them; went with Norwegian considering the biggest lot of those settled in that area. To balance that out and better compliment Rarity's personality, I lent Hondo some Austrian-German based on Audrey Hepburn and Cookie some Hungarian based on the Gabor sisters.
*I felt like having one other fullblood on the group, and seeing how Rainbow is an exuberant spitfire with a rainbow-color theme and a thirst for cider (not to mention a freckly redhead mom), I settled on Rainbow being all-Irish.
*For some reason, looking at Fluttershy, Dutch comes to my head, so I gave that to her dad. Lucky too, considering I made Fluttershy the tall one of the Six and Dutch people happen to statistically be the tallest in the world (well, the men, at least), so I figure it's a cute little justification for her height :P I also gave some English to both of them on the basis of Marilyn Monroe being a big influence on Fluttershy's voice. As for the Mrs.'s Scottish, that comes from Fluttershy's own underlying fiery side and also from Dianne Wiest, who I'm positive Mrs. Shy was modeled after.