The wings part, I don't know, maybe. Maybe not. Faust herself mentioned she wanted Twilight to surpass Celestia. Does this mean she was destined to become an alicorn from the start? Possibly. I don't know if Faust envisioned Twilight as an alicorn, or if what what ended up happening was what she really wanted or not. Point is, Princess Twilight isn't some sudden change Hasbro threw at us just for toys. It still is possible that adding wings was mainly for toy purposes, but since Twilight was already destined to ascend, they made it work.
We don't know how much of this was planned, and how much of it was about toys, but I at least believe it was largely planned, and the toy plans had little influence. At most, that's how she got her wings, but not how she achieved princesshood. Is that really a bad thing?
I like how it turned out. I think Twilicorn is adorable and if she was already destined for greatness, what harm is there at giving her wings while they're at it?