This came about from thinking about the Cutie Mark Crusaders, their talents and when they discover them.
I'd actually like their getting their marks to be a major arc spread across several episodes. I'd like to see it start with Luna appearing at a CMC sleep-over in the clubhouse (she literally crashes into the house for some reason, muttering something about down-drafts and sun-marked pranksters). As Applebloom is making good the damage, Luna tells them the stories of how she and Celestia got their cutie marks. She then gives them some wisdom about looking for the things that they already enjoy and seeing if they can find their true talent hidden in that..
The Singer
Sweetie Belle - I'd like her to find that her ability to sing is more powerful than just a musical talent; it's a magical talent too. I'd like for her to be a Spellsinger, a subset of unicorn who can create complex spells through music. They're unthinkingly rare, even Luna and Celestia can only recall a handfull of them, so Rarity can't find a tutor to help Sweetie to learn to use the ability. Twilight, who has read up on the subject (of course), so has thus become the world's only semi-expert on the abiltiy, takes her on as her first Personal Student.
This leads to an interesting confrontation with Diamond Tiara and Silver Spoon, who insist that the Personal Student of a Princess shouldn't hang around with common blank-flanks. This fits in with AB's and Scoot's fears too.
The Builder
Apple Bloom - She's a Shaper; she can use her Earth Pony magic to build structures or mechanisms from little more than scrap. This isn't a rare talent but it's more common amongst Rock Farmers. That's why Applejack (with some trepidation) lets Pinkie take Apple Bloom on as her apprentice; Pinkie uses that power to build her various contraptions like the Candy-Copter.
The way that I would like for this to happen is for Apple Bloom and the other CMCs to take part in a sort of Soap Box Cart rally. Apple Bloom uses gimmicks straight out of Bad Piggies to create a real gadget-mobile. They can climb steep slopes, float gently down under parasols and even fly short distances.
The Dancer
Scootaloo - She's all about acrobatics, agility and (much to her horror) dance. For her, it will be more about accepting this talent than discovering it as she wants to be 'awesome' like Rainbow. It takes somepony perhaps like Fluttershy to convince her that awesome is something you define for yourself.
As Scoot's ability is least-well-defined, it might be good if she was the last to get her mark and, maybe, to have her go through a phase where she wonders if her friends are leaving her behind.