I think the C7 idea is a bad one for the following reasons:
1) MLP has always been about lots of different ponies. They're more fun to play with in "herds", and the line is set up so you can buy a lot without breaking the bank(minimal accessories, relatively small price). The C7 thing doesn't match with how the line has always worked.
2) If the point of having a toy line is to sell as many of that toy as possible, limiting the choices to only 7 different items with only slight variations doesn't make sense.
3) MLP is not Barbie, and even if Hasbro wanted to take it in that direction, they're still doing it wrong. Barbie/Brats/whatever dolls may be released over and over, but they also get massive amounts of accessories, playsets, and other gimics to get you to buy the same doll over and over again. Ponies aren't getting much. The individual ponies are getting only one accessory each, and even the larger sets aren't getting all that much, just some plastic clothes and a handful of accessories. They also arent' supporting the line with a cartoon which really helps if you want to have kids "get to know the characters".
4) Parents and kids aren't stupid. Kids know that they're getting the same pony over and over again, even if they make it look a bit different every time. It's boring to play like that, especially since Hasbro doesn't seem to be making any good playsets or massive accessory sets. And what parent is going to spend money on the same thing over and over again? Parent's aren't clueless when it comes to ponies, and they're going to notice that their kid already has 3 Pinkie Pies and 4 Rainbow Dashes. How many kids are going to hear "you've already got that one" from their parents?
5) Hasbro already had a way to re-release the characters so kids could still get their favorites even after they had moved on to the next set. They gave them new poses and made them into the ponywear sets. They cost about a dollar more per pony, but you got a bunch of accessories with it. They also stuck re-releases in store exclusive packs, bonus packs, and special releases. It wasn't exactly popular with collectors, but it worked.
I think the C7 concept is going to kill the line. It discourages people from buying a lot of ponies, it's as simple as that. They either have to bring back the variety, or support the new direction properly. It's pretty half-baked as it is right now.